• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Materials and methods
 Anatomy of male genitalia...
 Comparative morphology of the male...
 Discussion
 Summary
 Literature Cited
 Figures
 Biographical sketch
 Copyright






Group Title: anatomy of the male reproductive tract of the cotton rat (Sigmodon hispidus) and comparisons with other muroid genera.
Title: An Anatomy of the male reproductive tract of the cotton rat (Sigmodon hispidus) and comparisons with other muroid genera.
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Title: An Anatomy of the male reproductive tract of the cotton rat (Sigmodon hispidus) and comparisons with other muroid genera.
Physical Description: Book
Language: English
Creator: Arata, Andrew A.
Publisher: Andrew A. Arata
Manufacturer: University of Florida
Publication Date: February, 1962
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Bibliographic ID: UF00091614
Volume ID: VID00001
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
        Page v
    List of Tables
        Page vi
    List of Figures
        Page vii
        Page viii
        Page ix
        Page x
    Introduction
        Page 1
        Page 2
        Page 3
    Materials and methods
        Page 4
        Page 5
        Page 6
        Page 7
    Anatomy of male genitalia of sigmodon
        Page 8
        Page 9
        Page 10
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        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
    Comparative morphology of the male genitalia of genera of muriod rodents
        Page 30
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    Discussion
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    Summary
        Page 97
        Page 98
    Literature Cited
        Page 99
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    Figures
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    Biographical sketch
        Page 223
        Page 224
    Copyright
        Copyright
Full Text










The Anatomy of the Male Reproductive Tract of

the Cotton Rat (Sigmodon hispidus) and

Comparisons with Other

Muroid Genera








By
ANDREW ANTHONY ARATA


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY









UNIVERSITY OF FLORIDA
February, 1962















ACKNOWLEDGMENTS


A debt of gratitude is expressed to the numerous people whose

help was essential to the completion of this study. Drs. Richard

Van Gelder and Sydney Anderson, American Museum of Natural History;

Dr. Emmet T. Hooper, Museum of Zoology, University of Michigan;

Dr. James N. Layne, University of Florida; Messrs. Dale E. Birkenholz,

Charles W. Myers, William 0. Wirtz III, and Larry Ogren all provided

specimens of various genera for dissection.

A special debt of gratitude is due to Mr. J. Howard Hutchison

for his time in preparing the drawing of the baculum of Sigmodon

hispidus, and to Dr. Clayton E. Ray for his stimulating conversations

about cricetids.

Advice and criticism from the following persons is acknowledged:

Drs. Archie Carr, Henry M. Wallbrunn, Carl D. Monk, and Robert M. De

Witt.

Finally, a sincere debt of gratitude is owed to Dr. James N.

Layne for his advice and counsel as committee chairman and for

indispensable help in preparation of this dissertation.














TABLE OF CONTENTS


Page

ACKNOWLEDGMENTS. . . . . . . . . . ...... ii

TABLE OF CONTENTS. . . . . . . . .....

LIST OF TABLES . . . . . . . . . . . . vi

LIST OF FIGURES. . . . . . . . . . . . vii

INTRODUCTION . . . . . . . . . . . . . 1

MATERIALS AND METHODS. . . . . . . . . . . 4

ANATOMY OF MALE GENITALIA OF SIGMODON. . . . . . . . 8

External Genitalia . . . . . . . . . 8

Phallus. . . . . . . . . . . . 8

General morphology . . . . . . . . . 8

Baculum. . . . . . . . . . . . 11

Functional morphology. . . . . . . . . 14

Accessory Glands . . .. .. .. 17

Preputial glands . . . . . . . . .. 17

Bulbo-urethral glands. . . . . . . . .. 17

Vesicular glands . . . . . . . . . 18

Ampullary glands . . . . . . . . . 18

Prostate glands. . . . . . . . . . 19

Testis, Epididymis, and Vas Deferens . . . . . 23

Urethra. . . . . . . . . . . . . 25

General Circulation of the Reproductive Tract. . . . 26


iii

















Table of Contents (Continued)


General Innervation of the Reproductive Tract .


Sympathetic nervous system .


Parasympathetic nervous system .


COMPARATIVE MORPHOLOGY OF TIE MALE GENITALIA


MUROID RODETS . .


Mesocricetus . .


Oryzomys . .


Oecomys. . . .


Nectomys . . .


Akodon . . .


Phyllotis. . . .


Nyctomys . . .


Peromyscus . .


Reithrodontomys. .


Neotoma . . .


Tylomys. . . .


Baiomys . . .


Ochrotomys . . .


Onychomys . . .


Synaptomys . .


Ondatra. . . .


Neofiber . . .


Microtus . . .


Pedomys. . . .


Pitymys . . .


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Table of Contents (Continued) Page

Clethrionomys. . . * # . # . & . . 75
Clethronoattus . . . . . . . . . . . . . 75


Mus . . . . . . . . . . *. . .. 80

DISCUSSION . . . . . . . .. . . . . 81

The Use of Genital Structures as Taxonomic Criteria. . . 81

Patterns of Morphological Variations in the Male
Genital Tract of Muroid Rodents. . . . . . 84

Structure of the phallus . . . . . . . 84

Accessory glands . . . . . . . . 85

Taxonomic Implications ....... . . . . . 92

SUMMARY . . . . . . . . . . . . . . 97

LITERATURE CITED . . . . . . . . 99

FIGURES. ........ . . . . . . 104

BIOGRAPHICAL SKETCH. . . . . . . . . . . . 223














LIST OF TABLES


Table Page

1. List of Species and Number of Specimens (in parenthesis)
Examined. ...... ....... . . . .. .... 6

2. Summary of the Variation in Accessory Glands of 24
Muroid Genera .......... ...... ..... 86













LIST OF FIGURES


Figure Page

1. External genitalia of male Sigmodon hispidus . . . 108

2. Base of the penis of Sigmodon hispidus. . . . . .. 110

3. External morphology of the glans penis of Sigmodon
hispidus. . .. . . . . . .. . . . 112

4. Lateral view and selected cross sections of the glans
penis of Sigmodon hispidus . . . . . . . . 114

5. Details of the internal structure of the glans penis
of Sigmodon hispidus. . . . . . . . . . 116

6. Dorsal views of the circulatory apparatus of the glans
penis of Peromyscus, Sigmodon, and Mesocricetus . . 118

7. Details of the glans penis of Sigmodon hispidus . . . 120

8. Dorsal views of the circulatory apparatus of the glans
penis of Neofiber, Ochrotomys, and Neotoma. . . . . 122

9. Several views of the internal portions of the glans
penis of Akodon . . . . . . . . . 124

10. Several views of the internal structure of the glans
penis of Rattus . . . . . . . . . . . 126

11. Baculum of Sigmodon hispidus. . . . . . . . 128

12. Synovial joint between shaft and median distal process
of the baculum of Sigmodon hispidus . . . . . . 130

13. Baculum and associated circulatory structures of a
six month old Sigmodon hispidus that had been castrated
at about one month of age . . . . . . . . 132

14. Male reproductive tract of Sigmodon hispidus. . . . 134

15. Basic functional changes occurring in the penis of
Sig~odon hispidus at erection . . . . . . . 136

16. Cross sections of the preputial gland of the Sigmodon
hispidus. . . . . . . . . . . . 138











List of Figures (Continued)

Figure

17. Cross sections of urethral glands of Sigmodon hispidus. .

18. Diagrammatic longitudinal section through caudal
region of male Sigmodon hispidus. . . . . . . .

19. Cross section of the vesicular gland of Sigmodon hispidus

20. Cross sections of the ampullary glands of Sigmodon
hispidus, . . . . . . . . . . . . .

21. Cross sections of the median ventral prostate gland of
Sigmodon hispidus . . . . . .....

22. Cross sections of the lateral ventral prostate gland of
Sigmodon hispidus . . . . . . . . .

23. Cross sections of the dorsal prostate gland of Sigmodon
hispidus . . . . . . . . . . . .

24. Cross section of the anterior prostate gland of Sigmodon
hispidus . . . . . . . . . . . .

25. Diagrammatic representation of the duct systems of the
accessory reproductive glands of Sigmodon hispidus in the
region of the prostatic urethra . . . . . . .

26. Testes and associated structures of Sigmodon hispidus . .

27. Distribution and variation in the course of the spermatic
artery on the surface of the testis in 7 pairs of
Sigmodon hispidus testes. . . . . . . ... .

28. Cross sections of the testis of Sigmodon hispidus . . .

29. Cross sections of the caput epididymis of Sigmodon
hispidus . . . . . . . . . . . .

30. Cross sections of the corpus epididymis of Sigmodon
hispidus . . . . . . . . . . . .

31. Cross sections of the cauda epididymis of Sigmodon
hispidus showing region of ciliated epithelium. . . .

32. Cross sections of the cauda epididymis of Sigmodon
hispidus showing region of unciliated epithelium. . .. .


viii


Stage

140


142

144


146


148


150


152


154


156

158


160

162


164


166


168


170










List of Figures (Continued)

Figure

33. Longitudinal section of the vas deferens of Sigmodon
hispidus. . . . . . . . . . . .

34. Cross sections of the urethra of Sigmodon hispidus
at different levels . . . . . . . .

35. Distributional pattern of the nerves to dorsal surface
of the glans penis of Sigmodon hispidus . . . .


Male reproductive tract of Mesocricetus . . . . .

Male reproductive tract of Oryzomys . . . . . .

Male reproductive tract of Oecomys. . . . . . .

Male reproductive tract of Nectomys . . . . . .

Male reproductive tract of Akodon . . . . . . .

Male reproductive tract of Phyllotis. . . . ..

Male reproductive tract of Nyctomys . . . . .

Male reproductive tract of Peromyscus . . . . .

Male reproductive tract of Reithrodontomys. . . . .

Male reproductive tract of Neotoma. . . . . ..

Male reproductive tract of Tylomys. . . . . . .

Male reproductive tract of Baiomys. . . . . . .

Male reproductive tract of Ochrotomys . . . .

Male reproductive tract of Onychomys. . . . . . .

Male reproductive tract of Synaptomys . . . ....

Male reproductive tract of Ondatra. . . . . . .

Male reproductive tract of Neofiber . . . . . .

Male reproductive tract of Microtus . . . . .

Male reproductive tract of Pedomys . . . . ..


36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.


Page


172


174


176

178

180

182

184

186

188

190

192

194

196

198

200

202

204

206

208

210

212

214











List of Figures (Continued)

Figure

55. Male reproductive tract of Pitymys. . . . . . .

56. Male reproductive tract of Clethrionomys. . . . .

57. Male reproductive tract of Rattus . . . . .

58. Male reproductive tract of Mus. . . . . . . .


Page

216

218

220

222














INTRODUCTION


In many animal groups, great importance has been attached to the

genitalia, especially that of the male, for purposes of classification.

In the Mammalia, classical taxonomy has not considered the genitalia,

but has been concerned mainly with osteological and dental characters.

This is not to say that genital characters have been unknown; rather

that, though certain elements were known, they have largely been

ignored until comparatively recent years.

The most distinctive element of the male genitalia, the phallus

and its bone, the baculum, have been described in many mammals over a

period of years. Most early works are descriptive, and few are of a

comparative nature. A vast literature exists on the baculum of mammals.

Most descriptions are scattered, however, and a few are inaccurate.

Periodically, attempts have been made to catalog the bacula of certain

taxa or of mammals of certain geographic regions. Important works of

this nature are those of Gilbert (1892), Chaine (1925), Burt (1936;

1960), Blair (1942), Hamilton (1946), Didier (1943; 1948; 1950; 1952;

1953; 1954), White (1953), and Anderson (1960).
Although the baculum serves as a useful tool for taxonomic work

at certain levels, its use is limited by its sporadic distribution

within the Mammalia. It is not present in the Prototheria or Metatheria

and is known from only six of fifteen Recent orders of Eutheria. Further,

in certain orders (i.e., Insectivora, Primates) not all genera possess











the baculum. On the other hand, the general morphology of the genitalia

may be compared between taxa at any level, or within taxa.

The phallus and the accessory glands offer a field for comparative

anatomical study that has been poorly exploited. From the early 1800's

numerous works have appeared describing the male genitalia of mammals

in various degrees of detail. Oudemans (1892) described part, or all,

of the genitalia of 50 mammalian genera, and summarized the literature

on accessory glands available at that time. Engle (1926) incompletely

summarized the literature and gave information on the accessory glands

of representatives of 16 orders. However, despite the extent of

early work on this subject, the only order that received a nearly

comprehensive coverage was the Insectivora (Kaudern, 1907; 1911).

In the Rodentia Tullberg (1899) discussed the male genitalia of

several genera in a sketcIh fashion. Only the Sciuridae have received

intensive study (Mossman, et al., 1932; Prasad, 1957). The more recent

work on the genitalia of rodents has dealt with forms widely scattered

throughout the order. Some of the more important of these papers have
dealt with: Aplodontia (Pfeiffer, 1956), Thomomys (Gunther, 1956;

1957), Rattus (Price, 1936), Mus (a number of early papers summarized
by Snell, 1941), Microtus (Hamilton, 1941; Delost, 1955), Neotoma

(Howell, 1926), Chinchilla (Beyerlein and Hillemann, 1952), Erethizon

(Mirand and Shadle, 1953), Myocastor (Hillemann, et al., 1958; Stanley

and Hillemann, 1960). Most of these studies are descriptive, with

little or no attempt at comparison with related forms.











A recent series of papers by Hooper (1958, 1959, 1960) on the

comparative morphology of the glans penis of members of the Cricetinae

has been of a different nature, however. Hooper has demonstrated that

clear distinctions in the phallus exist within the subfamily, and that

certain genera show closer affinities to members of other subfamilies

and families than to genera supposedly belonging to the same subfamily.

The purposes of this study are to determine the extent and the

nature of the variations occurring in the structures of the male geni-

talia of muroid rodents, and how they relate to the current taxonomic

arrangement. The anatomy of the male reproductive tract of a represent-

ative form (Sigmodon hispidus) has been studied in detail as a basis

for comparison with other muroids.














MATERIALS AND METHODS


Specimens of genera received from various sources were preserved

in different fluids. Only locally collected specimens of Sigmodon

hispidus were sectioned. In specimens to be used for histological

study the reproductive tract was removed as soon after death as possible,

oriented, and fixed in formalin or formalin, alcohol, and acetic acid

(FAA). For routine histology of the accessory glands and other soft

parts, paraffin embedding and staining with hematoxylin and eosin or

Van Giesen's and orcein was employed.

All genital tracts utilized for gross study were removed from

the specimens under a dissecting microscope. Fat and associated tissues

were teased from the tracts with finely ground steel forceps. Some

specimens were dissected while immersed in ether to facilitate the

elimination of fat from very small glands.

Whenever possible, dissection under a dissecting microscope was

used for examination of prostatic ducts and microanatomy of the glans

penis. In addition, specimens were mounted in collodion and handsections

made (Carleton, 1957; Pantin, 1959). Sections of 0.5 1.0 mm were thus

prepared and stored in clove oil. Staining of hand-cut sections was

accomplished in either hematoxylin and eosin or chlorazol black. It was

found that tertiary butyl alcohol could be substituted for chloroform in

the method described by Pantin (1959).











To examine the circulatory system, arterial and venous injections
were made with gelatin solutions of india ink (venous) and carmine

(arterial), following a circulatory flush with warm, isotonic saline

injected into the left ventricle of the living animal (De Santo, 1960).

For preparations of bacula, the standard two per cent KOH

macerating solution followed by staining with alizarin red and clearing

in glycerin was used (Anderson, 1960). Some bacula were prepared by

dissection rather than clearing, a technique more tedious but consider-

ably better for detailed examination of the baculum and adjacent parts

of the circulatory system.

Ground sections of the baculum were prepared by embedding the

bone in heated balsam on a slide and allowing the balsam to cool to a

glassy consistency. The specimen could then be ground by the use of

carborundum on a glass plate. The slide was then heated, the bone

removed and reversed, and the opposite side ground. This procedure

was repeated until the desired thickness was attained.

Approximately 50 male specimens of Sigmodon hispidus were used
in this study. The drawings of the microanatomy of the glans penis

represent information obtained from over 25 dissections of this organ.

The number of specimens of other genera studied ranged from one to

ten.(Table 1).










TABLE 1

LIST OF SPECIES AND NUMBER OF SPECIMENS
(IN PARENTHESIS) EXAMINED

Order: Rodentia

Suborder: Myomorpha
Superfamily: Muroidea
Family: Cricetidae
Subfamily: Cricetinae
Tribe: Cricetini
Mesocricetus auratus (2)

Tribe: Hesperomyini
Oryzomys Dalustris (10)

Oecomys tectus (2)

Nectomys alfari (2)

Tylomys fulviventer (2)

Nyctomys sumicrasti (1)

Reithrodontomys humulis (2)
Peromyscus gossypinus (4)

Ochrotomgs nuttalli (2)

Baiomys taylori (1)

Onychomys leucoiaster (1)
Akodon s. (1)
Phyllotis danrini (1)
Sigodon hispidus (50)

Neotoma floridana (3)

Subfamily: Microtinae
Tribe: Lemmini










TABLE 1--Continued


Synaptomys cooper (2)
Tribe: Microtini
Clethrionomys gapperi (1)
Ondatra zibethicus (5)
Neofiber alleni (4)
Pitymys pinetorum (3)
Microtus pennsylvanicus (2)
Pedomys ochrogaster (1)

Family: Muridae
Subfamily: Murinae
Rattus norvegicus (10)
Mus_ musculus (5)

Total number examined. . 117














ANATOMY OF THE MALE GENITALIA OF SIGMODON


External Genitalia

Externally, only the penile papillus and scrotum are visible.

The penile papillus is unpigmented, and the scrotum is black in breed-

ing adults. The median raphe is clearly visible, even in young animals

in which the testes are not scrotal. The scrotum is hairless ventrally

and thinly haired laterally.

The testes when fully scrotal protrude about 5 10 mm posterior

to the anus (Fig. 1), and are in contact with one another medially.

The tips of the cauda epididymides flare to give the fully mature

scrotum a slightly forked appearance. The caput epididymis is well

developed and surrounded by yellovish-green fat.

The lateral preputial glands are too large to fit within the

confines of the prepuce and encroach upon the ventral aspect of the M.

rectus abdominis.

Phallus

General morphology.-The phallus originates in the bulb of the

urethra. The urethra turns antero-ventrally (about 1000) and receives

blood from several sources to form the corpus cavernosus urethrae. The

corpus cavernosus is formed by the median union of the crurae which

originate on the posterior border of the ischium, along with the M.

ischiocavernosus with which they are intimately associated (Fig. 2).











The body of the penis is about 20 25 mm long, the dorsal border lying

on the ventral surface of the M. rectus abdominus (Fig. 2). The glans
penis is deflected ventrally at an acute angle.

The prepuce of the glans penis contains the preputial glands,

which consist of a small ventral pair and a larger lateral pair. The
surface of the glans is spined. The distal part (1/3 1/2) of the glans

is corrugated (Fig. 3) in the flaccid state.

Internally, the structure of the glans penis is complex (Figs. 4

and 5). The baculum lies in the middle of the glans, surrounded by

associated circulatory structures and erectile tissue. Lateral to the

shaft of the baculum are large blood sinuses, the penile blood sacs.

These are connected to the corpus cavernosus urethra, from which they

receive blood (Fig. 4). Circulatory tissue surrounds the whole distal

structure of the baculum (Figs. 4 and 5). The blood supply of the distal
structures is continuous with that of the penile blood sacs (Fig. 4).

The circulatory apparatus of the glans penis is drained by the dorsal
vein of the penis, which is formed by the Junction of large vessels

from the lateral aspects of the glans and confluent with the penile blood
sacs (Fig. 4). The circulatory apparatus of the glans penis is drained
by the dorsal vein of the penis which is formed by the junction of large

vessels from the lateral aspects of the glans and confluent with the

penile blood sacs (Fig. 6). The dorsal blood vessel is situated in a

depression on the dorsal surface of the base of the baculum (Fig. 6), and

cradled between the lobes of the corpus cavernosus penis in the body of
the phallus (Fig. 6).










The urethra terminates near the base of the median process of the

baculum. The lappet tips of the urethra lie on the broad shelf of

this median process and are separated by a ventral keel on the latter

(Figs. 4 and 5).

The penile blood sacs are connected by a muscle, M. suburethralis

penis, which lies under the urethra on the ventral side (Fig. 8).

Slips of this muscle insert upon the broad shelves of the median process

of the baculum, distally, and upon the ventral surface of the corpus

cavernosus penis at the insertion of the latter upon the base of the

baculum. Dorsally, a tendon, the dorsal tendon of the penis, connects

the dorsal surface of the corpus cavernosus penis at the base of the

baculum to the lateral processes of the distal portion of the baculum.

Erectile tissue is most abundant in the walls of the glans penis

at the distal end, becoming less well developed proximally (Fig. 4).

The surface of the glans is spined, each spine being situated in

a depression (Fig. 7). The spines appear to be formed of cornified

epidermal tissue. There are approximately 125 spines surrounding the

glans at any level near the distal end (Fig. 7). The circumference of

the corrugated surface of the distal end of the phallus in the erected

state is approximately double that of the flaccid condition.

Compared with the glans of other genera, Sigmodon. Mesocricetus,

Akodon, Neofiber and even Rattus, as well as many other cricetids and

murids (Figs. 6, 8, 9 and 10) stand in strong contrast to such genera

Peromyscus, Ochrotomys, Neotoma, and many New World cricetines.











Baculum.--The baculum of S. hispidus has been figured previously

by Hamilton (1946) and Burt (1960). However, neither of these illus-

trations is completely accurate, since some of the salient characters

of the structure are not shown.

The baculum consists of a proximal shaft, and three digitate

processes at the distal end (Fig. 11). At the broad base are two

rounded condyles to which are attached the M. corpus cavernosus. The

concavities of the base of the baculum are confluent with similar

concavities in the muscle and in which is situated the dorsal vein of

the penis and the urethra on the dorsal and ventral aspect respectively.

The dorsal vein, formed from several veins of the glans penis, originates

in the dorsal depression on the base of the baculum.

The shaft of the baculum is rod-shaped in very young animals and,

though it reaches definitive length early in development, the enlarge-

ment of the base occurs later, in the area of the attachment between the

bone and the M. corpus cavernosus penis and increases with the growth

of the muscle. The condyles in many old animals become rugose.

From the broad base of the baculum, the shaft tapers distally

(Fig. 11), terminating in a laterally flaring bulb in many, but not all,

specimens. The shaft is generally rounded (as reported by Burt, 1960),

but in some individuals appears more triangular, or, ovate. Hamilton

(1946) figures a baculum with a ". . prominent deep keel on the

ventral aspect." Burt (1960) did not observe such a keel. I have

examined over 50 specimens and, though some possess a very shallow keel,

none are as distinctive as that figured by Hamilton. Perhaps consider-

able variation exists in this character between the 34 recognized sub-

species.











The bony base of the shaft and the proximal portion of the shaft

is cancellous in some specimens. There is a narrow medullary cavity

running the length of the shaft. The nature of this cavity is the same

as that described for Rattus by Ruth (1934): "It is not a series of

haversian systems, but it is rather one large system in which the medullary

cavity represents the haversian canal. . ." The baculum of Sigmodon

appears to have the same growth pattern as that of Rattus, with a single

medullary cavity, growth in width being accomplished by appositional

growth of subperiosteal osteoblastic activity. Definitive size is

accomplished first in length, the base developing later. Diverticula

run diagonally from the medullary cavity to the periosteum.

It is the distal architecture of the baculum that is most

distinctive. Hamilton (1946) represented this tri-partite structure as

a simple trident-shaped affair when viewed dorsally. Burt (1960) also

showed the digital processes as a single trident, but in a bit more

detail. Although the orientation is not stated in the figure, it appears

to be a dorsal view.

The median process is the most ventral and extends from the axis

of the shaft at about a 100 angle. It terminates in a dorsallydirected

hook, bending at about a 700 angle. On the proximal ventral surface of

this process are two laterally flaring shelves, separated by a small

keel (Fig. 11). Though the major portion of this process ossifies late

in life, I have not seen ossification of the shelves and keel though I

have examined some very large specimens. The two lappet tips of the

urethra lie on the lateral shelves, being separated, and in the flaccid

condition blocked, by the central keel.











The two lateral processes are in contact with one another

proximally on the dorsal side of the median process (Fig. 11).

All three digital processes will ossify with advanced age. The

two lateral processes do not necessarily ossify concurrently. Some

specimens will show both lateral processes ossified, some only one.

The site of ossification is in the central core of the process close to

the distal end.

An interesting feature of the structure of the baculum is that a

synovial joint (Fig. 12) exists between the digitate processes and

the shaft. This movable joint has apparently not been noted previously

and, paradoxically, is not in accord with the generally assumed sesmoid

nature of the bone. Neither are the facts of ossification demonstrated

in Rattus by Ruth (1934), which are apparently identical in Sigmodon.

Ruth demonstrates an unusual bony formation for the shaft in which

osteogenicc cells become active in laying down osteoid substance before

any marked differentiation of surrounding tissues can be observed an

endo-blastemal ossification." From my observations on the form and

development of the baculum of Sigmodon, I see no point at which the

development differs from the description of Rattus by Ruth (1934).

The similarities of other parts of the phalli substantiate the fact

of their similar origin.

The development of the baculum is apparently under hormonal control.

Figure 13 illustrates the baculum of a six-month-old Sigmodon hispidus

that was castrated when less than a month old. The form of the baculum

is that of a juvenile animal. Normal development of the associated











circulatory structures is apparent however. Normal six-month-old

animals of this species would have a baculum similar to that illustrated

in Figure 11.

Functional morphology.-The great morphological diversity existing

between the varied penile types in the Cricetidae prompts one to specu-

late regarding the function of such elaborate accessory structures as

possessed by Sigmodon. The simple nature of a phallus such as that of

Peromyscus would seem to be equally simple in function. The glans is

elongate and strengthened by the spine-like baculum. The urethra lies

ventrad of the baculum and is poorly supplied with erectile tissue.

The functional nature must necessarily be that of a narrow-gauge tube,

the insertion of the penis into the vagina being aided by the rigidity

supplied by baculum. In the short, squat glans of Sigmodon (as well as

numerous other genera with a trident-shaped baculum) no such simple

functional explanation seems to suffice. The operation of the baculum

only becomes apparent when the glans is considered as a morphological

unit. In all cases in which a trident-shaped baculum is present, it is

accompanied by the accessory circulatory structures previously described.

Vascular tissue surrounds the whole distal end, and the sizable penile

blood sacs constitute a large portion of the mass of the glans. The

tendon on the dorsal aspect of the baculum, the synovial joint at the

junction of the shaft and distal processes, and the sub-urethral muscle

must all be considered.

In the flaccid state the corpus cavernosus urethra and corpus

cavernosus penis are not engorged with blood, and the erectile tissue











of the glans is relaxed. The penile blood sacs are unexpanded, with but

a small amount of blood coursing through them and around the distal tips

of the baculum. An equilibrium is established between the dorsal tendon

of the penis and the tendons of the M. suburethralis penis connecting

the distal portion of the baculum to the corpus cavernosus penis on the

ventral side. The resulting position of the distal processes of the

baculum is such that the lappet tips of the urethra lie upon the broad

shelf of the median process, separated by the strong ventral keel. A

strong ventral flexure is present at the junction of the glans to the

body of the corpus cavernosus penis (Fig. 14).

In order to induce erection in the penis of freshly killed
Simnodon, the following techniques were employed. The base of the penis

was ligatured, and fluid or air under pressure (controlled by mouth

using a small diameter rubber tube) was forced into the dorsal vein of

the penis and/or the body of the corpus cavernosus penis. The penis

straightened, the glans falling in the same plane as the body of the

penis. The penile blood sacs became distended and the distal processes

of the baculum turned dorsad. This was accomplished by the relaxation

of ventral pressure due to the distortion in the M. suburethralis

accompanying the enlargement of the penile blood sacs to which they are

attached. The dorsal tension produced by the dorsal tendon of the penis

was increased as a result of the straightening of the glans (Fig. 15).

The distal processes of the baculum were forced apart slightly by the

engorging of their respective vascular sheaths. When the dorsal motion

of the distal processes is accomplished, the lappet tips of the urethra

are forced from the obstructing keel of the median process, and the











urethral orifice is unimpaired. If this dorsal flexure of the distal

processes did not occur the semen would not be afforded a free path into

the vagina. The urethral orifice is blocked in the flaccid state.

Other changes occurring upon erection of the penis are the

elevation of the penile spines located in pockets in the flaccid state

and the expansion of the glans to nearly double its size in the non-

erect state (Fig. 15). These two phenomena probably serve to secure the

position of the glans and dilate the vagina. There may be some "lock-

and-key" relationship between the dorsally flexed fork of the baculum

and the vagina of the female, but I was unable to find any such associ-

ation.

In addition to the function already ascribed to the penile blood

sacs, a further function seems probable. The usual relationship of

arterial and venous structures fail in the penis. Though I have not

been able to find them in Sigmodon, "sluice valves," and various forms

of hydraulic controls have been described in the penile circulation of

dogs (Christensen, 1954), man, and certain vespertilionid bats (Wimsatt

and Kallen, 1952). Some of these include expanded blood sinuses about

the baculum (dog and bats). Although these are quite probably not

homologous with the penile blood sacs of Sigmodon, they do seem to be

analogous. To maintain a constant vascular pressure in the penis, some

sort of hydraulic control is necessary. The "sluice valves" described

by Christensen (1954) is one method, another would be maintenance of

pressure by a sac-like arrangement operating on the principle of a

water bulb on a hydraulic pump.











Accessory Glands


Preputial glands.--These glands lie in the tissue of the prepuce

(Fig. 7). There are two pairs, a small ventral pair that is completely

within the confines of the prepuce, and a larger lateral pair that

encroaches upon the ventral border of M. rectus abdominis (Figs. 3 and

14). Each of the four glands is drained by a single duct. The small

ventral glands measure about 10 x 3 mm in greatest length and width,

respectively. Corresponding measurements for the larger pair are

18 x 5 mm.

The preputial glands are modified sebaceous glands. The large

polyhedral cells are best seen in the basal part of each unit, prior to

degeneration and formation of sebum. The nuclei are centrally located

in the secretary cells and the ducts are lined with squamous epithelium

(Fig. 16).

Bulbo-urethral glands.--These paired, tubulo-alveolar glands lie

anterior and lateral to the urethral bulb (Fig. 14). Each gland is

pear-shaped and is drained by a single duct. The glands are bordered by

the M. bulbocavernosus (caudad), the M. ischiocavernosus (cephalad), and

the M. externa caudae media mediallyy). The ducts pass between the

M. ischiocavernosus and M. bulbocavernosus to enter the dorso-lateral

walls of the urethra just anterior to the urethral bulb. The ducts

pass through the tissues of the membranous urethra to enter the lumen

at the point at which the urethra turns ventrad to form the penile

urethra. Each of these glands measure about 5 x 6 mm.











The secretary cells of the bulbo-urethral glands average 30 x 20

microns. When stained with hemotoxylin and eosin the nuclei are very

dark blue and the cytoplasm light pink. The nuclei are situated at the

base of the cell adjacent to the well developed basement membrane

(Fig. 17).

Vesicular glands.-The vesicular glands (Fig. 18) are the largest

of the accessory glands of Sigmodon. They are situated dorsad of the

bladder and form the most anterior portion of the tract. Not infrequently

they will be pushed together by pressure from the caecum of the gut.

The vesiculars are recurved, lumpy, and frequently lobate along the

greater curve. From the duct to the terminal portion along the greater

curve they may measure as much as 40 mm. The maximum thickness is

generally about 10 mm. Each gland is drained by a single duct, which

enters the urethra dorso-lateral to the ampulla.

The vesicular glands are covered by a thick sheath of connective

tissue, beneath which a thick layer of smooth muscle is present. The

mucous membrane is thrown into an amazing series of folds which provides

large secretary surface (Fig. 19). The secretary cells are elongate

(15 x 5 microns), and the nuclei situated at the basal portion adjacent

to the basement membrane. The waxy secretion is eosinophilic.

Ampullary glands.-These paired glands lie directly anterior to the

neck of the bladder (Fig. 14). They are closely associated with their

respective vas deferens and are contained within the same connective

tissue sheath. The glands are the smallest of the accessory glands,

the pair measuring about 6 mm in width, and about 4 mm in thickness

at maturity.










These are branched tubulo-alveolar glands. The epithelium is

heavily contorted, but owing to the small size of the glands, the

secretary surface is not extensive. The individual secretary cells

average 10 15 microns (Fig. 20). These glands are drained by

numerous ducts, as many as 14 to a gland, which enter the vas deferens

and vestibule of the ampulla.

Prostates.-These are the most confusing glands in the reproductive

tract. They are extensive, large in number, variable in color, inconstant

shape, and the homologies of glands designated as prostates in different

mammalian groups are not clear.

Walker (1910) described the glands that lie in the lesser curve

of the vesiculars as "coagulating" glands. He emphatically denied the

association of these with the prostatic series. The name "coagulating"

has been used since that date by most authors for these glands. Price

(1936) demonstrated that the prostates of Rattus arose embryologically

from three cords, destined to be the three main prostatic groups. The
"coagulating" are the most anterior of these three lobes, and are

therefore, prostates. Price (1936) termed these three prostatic groups

"posterior," "mid," and "coagulating." Hamilton (1941) discussing

Microtus used the term "ventral lobes" and "ventro-lateral" lobes. The

"ventral" lobes of Hamilton are however, the ampullaries, not part of

the prostatic series (as can be seen from his illustration). The

"ventro-lateral" lobes of Hamilton are the "coagulating" glands of Walker.

The difficulty involved in the naming of these glands is especially

great when comparing different genera, whose prostatic compliment may not

be the same.










The prostates are clearly divisible into three major groups in
Rattus (Price, 1936), Sigmodon. and many of the genera examined in

this study, and I have chosen to designate these groups as "anterior,"
"dorsal," and "ventral."

The anterior prostates correspond to the "coagulating" of
Walker (1910), Price (1936), and Snell (1941); and the "ventro-lateral"

of Hamilton (1941). I have not used "coagulating" because we are not

certain of the function of this, or for that matter, any other accessory

gland. I have not used "ventro-lateral" because there are ventral and

lateral prostates other than these. I have chosen "anterior" because

of all prostates these are the most anterior, and because the ducts of

these enter the anterior portion of the prostatic urethra.

The "dorsal" prostates are the same as those similarly designated

by Sneed (1941) and are the "mid lobe" of Price (1936). Hamilton (1941)

did not mention these glands in Microtus though they are present. These

glands are on the dorsal border of the prostatic urethra.

The "ventral" prostates are the "posterior prostates" of Price
(1936), the "prostates" of Walker (1910), and the "ventral" prostates of
Snell (1941). As previously mentioned, the "ventral" prostates of
Hamilton (1941) are ampullary glands. These glands lie on the ventral

surface of the prostatic urethra, posterior to the bladder. In Sigmodon.
and many other muroid genera, there are at least two sets of these.

The two pairs of the ventral prostates found in Sigmodon hispidus
consist of a median and lateral pair (Fig. 3). The former lies posterior

to the bladder. The glands are elongate and filiform. At the base of

each gland 8 10 tubules are visible, and sections of the prostatic











urethra indicate that there may be a corresponding number of ducts from

each of the glands. The glands are highly irregular in shape, twisted

about fat tissue, and pushed against the bladder or the vesiculars.

When straightened, each gland may be 15 25 mm long at maximum develop-

ment. As many as 50 75 tubules may be present at the terminal portion.

The ducts of these glands enter the ventral wall of the prostatic

urethra caudad and slightly ventrad to the neck of the bladder. These

glands are white when preserved in formalin or FAA.

The tubules are lined by columnar epithelium, the cells measuring

20 25 microns in length and 10 15 microns in breadth. The mucous

membranes are thrown into heavy folds (Fig. 21). The smooth muscle

between the tubules is not extensive. These glands do not section

easily, due, apparently, to the crystalline nature of the secretion

as it is precipitated by the fixative. The tubules of this gland are

loosely bound together by connective tissue.

The second pair of ventral prostates, equal in size and number of

tubules to the median pair lies lateral to the latter. The ducts of

these glands enter the ventral wall of the prostatic urethra lateral

to the neck of the bladder. As few as seven and as many as nine ducts

are present in each member of the pair. These glands assume a reddish

to purple color when preserved in formalin or FAA.

These glands are compound tubular (as many as 75 tubules present

at the terminal edge) glands, and closely resembles the pair of median

ventral prostates (Fig. 22). The secretary epithelial cells are more

elongate however, averaging 25 30 microns in length.










The small leaf-like dorsal prostate glands lie at the dorso-

anterior border of the prostatic urethra (Fig. 23). The colon passes

medially between the members of this pair. The glands are compact,

and bound tightly in a sheath of connective tissue. In the adult

each gland is about 7 x 5 x 2 mm in length, width, and thickness,

respectively. Each gland drains into the dorso-anterior wall of the

prostatic urethra through four to six ducts.

The dorsal prostate glands are not filiform, the tubules being

only visible upon dissection. About 15 tubules can be distinguished

in each of these glands. The tubules are of a smaller calibre than

those of the ventral prostates, and the mucous membrane is not as

heavily folded. The columnar epithelial cells are lower, averaging

15 20 microns, and the smooth muscle is proportionately thicker.

The secretion has a granular consistency.

The paired anterior prostate glands lie in the lesser curve of

the vesicular glands (Fig. 14). They consist of long filaments fre-

quently lying on either medial or lateral surfaces of the vesiculars,

or both. The tubules are large, averaging 3 5 times the diameter

of those of the ventral prostates. There may be from 25 35 tubules

in each gland of the pair. These are drained by anastomosing ducts

which lie adjacent to the duct of the corresponding vesicular gland

(Fig. 25).
Histologically, the anterior prostate glands are quite similar

to the other prostate divisions. The compound tubules are larger, how-

ever, and the mucous membranes are not as extensively folded. The










columnar epithelial cells are small, averaging 15 20 microns in

length (Fig. 24). The smooth muscle is not as extensive as that of

the dorsal prostates. The secretion appears to be somewhat granular

like that of the dorsal prostates.

Testis, Epididymis and Vas Deferens

The testis of Sigmodon hispidus is a large, oval, compound

tubular gland (Fig. 26). In a fully mature individual the testis may

measure up to 25 mm in length by 15 mm in width. The tunica albuginea

is pinkish white in a living animal. The course of the superficial

testicular artery on the surface of the testis is very tortuous.

Harrison (1949) figures radiograms of injected testicular arteries for

numerous genera of mammals and compared the distribution of this

artery. The distribution of this artery in Signodon, though quite

variable (Fig. 27), is very similar to Harrison's illustration for this

vessel in Rattus. Although Harrison commented upon the possible

taxonomic utility of this artery, the course taken by it is variable

within a species and, in the case of the muroid rodents, too similar in

many genera to be of usefulness. Its pattern does seem to differ

significantly between different orders of mammals, however (Harrison,

1949).

The cremaster muscle surrounds the testis in adult specimens. The

fibers of the cremaster originate in the region of the inguinal canal

and terminate on the testis and scrotum. The fibers are directed

posteriorly and are most dense along the dorsal border of the testis.

The cremaster receives blood from a branch of the external spermatic

artery.










The testis is divided into numerous lobules separated by projections

of the tunica into the body of the testis. The seminiferous tubules of

these lobules join at the rete testis, then form efferent ducts which
drain the testis. The seminiferous tubules average 210 microns in cross

section. A vell-developed basement membrane is formed (Fig. 28).

The Sertoli cells are round to polyhedral, about 10 microns in diameter.

The nuclei of these cells are large (4 5 microns) and centrally
located.

The caput epididymis is large, capping the cephalic pole of the

testis (Fig. 26). It is divided into eight lobules, the first of which

receives the vasa efferentia. I could only recognize two efferent

ducts in my material of Sigmodon. Mus (Snell, 1941) and Myocaster

(Stanley and Hillemann, 1960) are reported to have five to six such

ducts. The first lobule of the caput epididymis is a deep purple

color in formalin preserved specimens, the remaining seven lobules are

a light lavender. The epididymal ducts of the caput are large, averag-

ing 0.5 1 mm in diameter (Fig. 29). The epithelial lining of these

tubules is columnar, the cells up to 30 microns long. The nuclei of

these cells are situated at the base of the cells along the well
developed basement membrane.

The corpus epididymis runs along the median aspect of the testis.

In the corpus the fibrous connective sheath common to all parts of the

epididymis is well developed (Fig. 30). In a single cross section of

the corpus epididymis, the ductus epididymi is traversed 20 30 times,

so convoluted is this tube. The epididymal duct is 150 170 microns

in diameter through the corpus. The columnar epithelial cells average

23 microns, and have their nuclei located basally.
24










The large cauda epididymis is located slightly lateral, but caps

the posterior pole of the testis (Fig. 26). The tubules are visible to

the naked eye in sexually mature specimens, being as much as 1 mm in

diameter. They average somewhat smaller than the massive tubules of

the caput. The tubules of the cauda epididymis are lined by ciliated

columnar epithelium near the formation of the vas deferens (Fig. 31),

or by simple columnar epithelium in the major portion of the structure

(Fig. 32).

As the deferent duct straightens and leaves the corpus epididymis

(Fig. 26) it forms the vas deferens which eventually drains into the

prostatic urethra. This duct passes medially along the testis and

enters the abdominal cavity through the inguinal canal in association

with the nerves and blood vessels of the testis and epididymis.

The epithelium of the vas deferens is of the pseudostratified

ciliated type. A vell-developed lamina propria is present containing

many elastic fibers (Fig. 33). There is a layer of longitudinal smooth

muscle proximal to the lamina. A median, thick layer of mixed muscle

fibers (circular, oblique and some longitudinal) is present, surrounded

by a thinner layer of longitudinal muscle. This is almost identical to

the condition described in Myocastor (Stanley and Hillemann, 1960).

Urethra

The urethra in the male, forming a common duct for the urine and

the products of the reproductive organs, is differentiated into prostatic,

membranous, and cavernous (penile) portions.











The prostatic urethra receives the neck of the bladder, the

ampullae, and the ducts of prostate and vesicular glands.(Figs. 25

and 34). The illustration of this region in Mus provided by Snell

(1941) would be indistinguishable from similar sections of Sigmodon.

The duct systems of the various glands entering this region have been

described under the descriptions of the respective glands.

Slightly posterior to the region of the prostatic urethra, the

nature of the urethra changes. Its body is surrounded by a mass of

striated muscle, the sphincter urethrae membranaceae. Between the

muscular wall and the lumen, a mass of loose, simple alveolar glandular

tissue forms the diffuse urethral glands (Fig. 17). A small amount of

smooth muscle is present in the lamina propria. The lining of this

region of the urethra is psuedostratified columnar epithelium.

After receiving the ducts of the bulbo-urethral glands and the

artery of the penis, the urethra turns ventrad and joins the crurae of

the penis. The urethra, now possessed of cavernous and erectile tissue

is known as the corpus cavernosus urethrae. The urethral diverticulae

described for Mus (Snell, 1941) are not found in Simodon.

The lining of the penile urethra is stratified columnar epithelium.

The penile urethra terminates in two lappet tips, associated with the

median process of the baculum as previously described.

General Circulation of the Reproductive Tract

The circulatory supply of the accessory glands, urethra and penis

is provided by branches of the hypogastric trunk.











The superior vesicular artery gives off branches to the following

glands: vesicular; ampullary; dorsal, ventral, and lateral prostates.

In addition, branches also supply the vas deferens and the bladder.

The inferior vesicular artery has a similar distribution, but is not as

large.

All structures mentioned above are drained by veins which unite

to form the superior vesicular vein.

The preputial glands receive their blood supply from the superior

epigastric artery and the superior external pudendal artery. They are

drained by the superior external pudendal vein.

The bulbo-urethral glands are supplied by a small branch of the

artery of the urethral bulb, which in turn, is a branch of the artery

of the penis. The veins from these glands drain into the vein of the

urethral bulb which is continuous with the internal pudendal vein.

The internal pudendal artery gives off a branch, the artery of

the penis, which supplies the phallus and associated structures. The

artery of the penis gives off the following branches:

Artery of the urethral bulb this supplies the urethral bulb
and hence the corpus cavernosus urethrae and the bulbo-urethral
gland.

Urethral artery to the corpus cavernosus urethrae.

Deep artery of the penis to the M. corpus cavernosus penis and
the M. ischiocavernosus.

Dorsal artery of the penis to the surface of the corpus
cavernosus penis and surrounding connective tissues.

The corpus cavernosus penis of the body of the phallus is supplied

by the deep artery of the penis. The urethral artery and the artery of











the urethral bulb provide blood to the corpus cavernosus urethrae, which

in turn supplies blood to the associated circulatory structures of the

glans penis.

The blood of the penis is drained primarily by the dorsal vein of

the penis, which flows into the pudendal plexus at the base of the penis.

The blood from this plexus flows into the internal pudendal vein, to

the common iliac vein.

The testes are supplied by the spermatic arteries. These arise

from the dorsal aorta posterior to the renal arteries. The spermatic

arteries divide into external (to cremaster muscle) and internal branches.

The internal spermatic divides into the epididymal and testicular

arteries. The vas deferens, as previously noted, receives blood from

a branch of the superior vesicular artery.

The testes and epididymides are drained by the complex pampiniform

plexus, which eventually drains into the renal vein.

General Innervation of the Reproductive Tract


Sympathetic nervous system.-The prominent nerves of the male

reproductive tract are branches of the hypogastric plexus. This branches

to form two lateral plexuses on either side of the prostatic urethra.

The following smaller plexuses are branches of the pelvic plexuses:

Vesicular plexus innervates the vesicular glands, bladder,
ampullary glands, and vas deferens.

Prostatic plexus innervates the prostate glands and the
membranous urethra.

Further subdivisions of the pelvic plexuses join with branches of

the pudendal nerves (parasympathetic) and pass to the penis.










Parasympathetic nervous system.-The pudendal nerve receives

fibers from several sacral nerves. Branches extend to the scrotum, the

bulb of the urethra, M. bulbocavernosus, and penis. The final branch

of the pudendal nerve forms the dorsal nerve of the penis (receiving

sympathetic fibers from the prostatic plexus) and is distributed over

the surfaces of the corpus cavernosus penis and to all structures,

superficial and deep, of the glans penis (Fig. 35).














COMPARATIVE MORPHOLOGY OF THE MALE GENITALIA

OF MUROID RODENTS


There are available descriptions and illustrations of the complete

male genitalia for but three of 99 currently recognized genera of

cricetid rodents. These are Mesocricetus auratus (Cricetinae,

Cricetini), Neotoma sp. (Cricetinae, Hesperomyini), and Microtus

pennsylvanicus (Microtinae, Microtini). Such a dearth of information

is disappointing when one considers the vast literature that deals with

the baculum alone. Comparison of the reproductive structures of as

many genera as possible was made to determine the extent of variation

occurring in muroid rodents and the relation of these findings to the

present concept of taxonomy based upon other criteria (Table 1).

Several introductory comments are necessary in order that the

descriptions may be viewed in proper perspective. First, the genera

included are not truly of equal taxonomic rank. For example,

Peromyscus is composed of some 27 species, many rather diverse, which

may be subdivided upon further examination. On the other hand,

Ochrotomys is monotypic, until recently recognized as a subgenus of

Peromyscus. Onychomys and Baiomys include but two species each. As

it was obviously impossible to treat all the species of each genus

included, I have examined one species of each genus (Table 1), fully

realizing that further study on the larger genera may necessitate

additions to, or revisions of, certain of the conclusions drawn from

the present study. Secondly, variation within each form must be










considered. I have examined the genitalia of 50 specimens of Simodon

hispidus, and have found no variation in the basic number and morphology

of the accessory organs. This has also been the case with Ondatra.

Neofiber, Oryzomys and several other genera for which at least several

specimens were available. On this basis, therefore, I feel that the

data obtained for genera for which but a single adult specimen was

available are trustworthy. The number of specimens examined for each

genus is listed in Table 1.

Age and seasonal changes in forms where a seasonal reproductive

cycle occurs are other important sources of variation. Unless otherwise

noted, descriptions and illustrations are based upon adult specimens

with scrotal testes and in which the tubules of the cauda epididymis

were visible, two usual criteria for a fecund conditions in male rodents.

It is difficult, and probably fallacious, to give accurate measurements

of glands subject to such seasonal variability. Where given, the

measurements in this section are for the greatest length by the greatest

width of organs, unless otherwise specified. Care was taken that a

similar orientation of glands was used in all measurements.

Unless otherwise stated, the bulbo-urethral glands and their

duct systems are similar to those found in Sigmodon. These glands are

so alike in all genera examined that individual descriptions are not

warranted.

With certain forms it is difficult to determine if a prostate

is bilobed, or whether two pairs are involved. I have attempted to follow

a conservative course, so that unless the glands were distinctly separate

with clearly unique duct systems, I have considered them to constitute











a single bilobed gland. The basic morphology of the gland (e.g., the

diameter of the tubules) was considered in making such decisions.

Of all the genera examined, only Rattus. Mus, and Mesocricetus

shoved variation in the nature of the accessory glandular structures.

In one specimen of Mesocricetus only one vesicular gland was present.

In a specimen of Rattus, the number of prostates was not equal on the

left and right sides of the urethra. These are also the only genera

examined that were from inbred strains of laboratory animals. Osteo-

logical variations in such strains of Rattus are well known, so there

is little reason that genital structures might not suffer similar

aberrations. Therefore, though I have figured what appeared to be

the "normal" condition, I have reservations about the descriptions of

these three genera.











Mesocricetus Nehring 1898

(Fig. 36)

The phallus is of the complex type, and the surface of the glans

is spined. The accessory circulatory structures are well developed

(Fig. 6). The baculum has been described by Didier (1948) and Callery

(1951). Caller (1951) discusses osteogenesis of this bone and illus-
trates five stages in the development. The median distal process is

ventrally depressed, the urethra being completely blocked by this

process. The median process is usually the largest of the three digital

processes in animals possessing a trident-shaped baculum, but this is

not the case in Mesocricetus.

The accessory glands have been described in part by Ortiz (1947).

The ducts of the prostates are considered, but there is no mention of

the number of lobes, their extent, and other aspects of interest from

a taxonomic standpoint. The discussion of the embryology of the tract

and hormonally induced variation is noteworthy.

Preputial glands were not present in the specimens examined.

The vesicular glands are large and strongly recurved ventrally.

They are lumpy and irregular in shape, being quite bulbous on the

median surface near the ducts. A single duct from each gland enters

the anterior aspect of the prostatic urethra dorsal and lateral to the

vas deferens. The greater curve of the gland is heavily lobate, some

of the lobes being compoundly branched. Although a number of genera

exhibit some degree of location of the vesicular, the condition is most

pronounced in Mesocricetus.











The ampullary glands are large and lie at the point of contact

of the two vasa deferentia. The glandular tissue is not as tightly

bound by connective tissue as in Sigmodon. and consequently forms a

more amorphous mass.

Three pairs of prostates are present in Mesocricetus. A single,

elongate (12 x 5 mm) pair of ventral prostates lies lateral and caudal

to the bladder. The ducts enter the ventral wall of the prostatic

urethra lateral to the neck of the bladder. The paired dorsal prostates

are situated on the antero-dorsal wall of the prostatic urethra through

which the ducts pass. They encroach upon the dorsal margin of the

vesicular glands for a short distance. The colon passes between the

two lobes of this gland. The paired anterior prostates are located

within the lesser curves of the vesiculars and in contact with the

lateral borders of the latter glands. The ducts of the anterior pros-

tates, two on each side, enter the prostatic urethra adjacent to the

vesicular ducts.

The testis, epididymis and vas deferens are not qualitatively

different from those of Sigmodon. The entire epididymis is invested

with yellow fat.











Oryzomys Baird 1857

(Fig. 37)

The phallus is of the complex type; the surface of the glans is

spined. All accessory circulatory structures are well developed as

are the tendons and the M. suburethralis penis. The general appearance

is not unlike that of Sigmodon. The major differences lie in the

nature of the baculum, where the condyles are not as well developed as

in Sigmodon, and the cartilaginous distal processes are more attenuate.

One old individual examined had the distal processes partially

ossified. Hamilton (1946) first illustrated the baculum for 0. palustris;

Didier (1953) figures the shaft only. Burt (1960) figured this element
for 0. melanotis. Burt's illustrations are the best available. The

shaft is narrow at the distal end, flaring broadly at the base. The

dimensions of the processes vary in the different species.

A single pair of preputial glands is present. These are large

and flaring at the proximal end. The main bodies of the glands lie on
the sides of the glans penis. Each is drained by a single duct that

opens at the distal, lateral edge of the prepuce.

The vesicular glands are large and recurved in Oryzomys. with

the tips in contact with the base of the gland. They are very lobulated.

Laterally, the gland appears to be a solid mass but its recurved nature

is readily apparent upon dissection. The single duct of each gland

enters the prostatic urethra immediately lateral to the vas deferens.

The ampullary glands are compact, each being adjacent to the

respective vas deferens. Each gland is drained by numerous ducts,

opening into the vas deferens just distal to the ampulla.











Four pairs of prostates are present. The two pairs of ventral

prostates consist of a median pair (10 x 3 mm) lying caudad of the

bladder, and a more lateral, bulbous pair (6 x 5 mm) situated on either

side of the median pair. The ducts of the former enter the urethra

posterior to the neck of the bladder, while those of the latter enter

slightly more laterally. The median ventral prostates are white in

formalin or FAA, while the lateral ones are red in the same. A single

pair of elongate dorsal prostates (8 x 4 mm) is situated on the dorsal

surface of the urethra, encroaching anteriorly onto the dorsal border

of the vesiculars. The colon passes medially between the members of

this pair. The ducts enter the antero-dorsal wall of the prostatic

urethra. The anterior prostates are filiform, fanlike glands, lying

upon the median surfaces of the vesiculars (Fig. 37, B). They are

drained by two ducts on each side, the ducts entering the urethra

lateral to those of the vesiculars.











Oecomys Thomas 1906

(Fig. 38)

I was able to obtain only the proximal portion of the tract

so I cannot comment upon the phallus, preputial or bulbo-urethral

glands. Hooper (1959) mentions that the phallus is complex in nature,

but does not elaborate.

The vesicular glands are lumpy and recurved. The median border,

as well as the greater curve, are both irregular in shape. The recurved

tip is strongly notched. Each gland is drained by a single duct

entering the urethra dorsal and lateral to the ampulla.

The ampullary glands lie upon the corresponding vas deferens to

which numerous ducts pass in the region of, and immediately preceding,

the ampulla.

Four pairs of prostates are recognizable in this genus. An

elongate (9 x 3 mm), median pair of ventral prostates lies directly

caudad of the bladder, and a second, more bulbous (3 x 3 mm), lateral

pair is located on the sides of the prostatic urethra. The median

pair is white in formalin, the lateral pair a reddish purple color.

The ducts of the median pair enter the prostatic urethra posterior

to the neck of the bladder, the other pair enter the urethra through

the lateral walls. The dorsal prostates are represented by a pair

of compact glands at the anterior end of the urethra. The ducts enter

the urethra through the antero-dorsal wall. The anterior prostates

are a loose, filiform set of glands lying in the lesser curve of the

vesiculars. These are drained by a pair of ducts on each side that

enter the urethra lateral to the ducts of the vesiculars.

37











Nectomys Peters 1861

(Fig. 39)

The phallus of this genus has not previously been described

although Hooper (1960) mentioned that it was of the complex type. The

glans is spined, and its internal architecture is basically similar to

Sigmodon. The distal processes of the baculum and associated circulatory

structures are large and bulbous. The lateral processes are larger than

the median, similar to those of Mesocricetus (Fig. 6). The median

process is smaller, ventrally depressed, and blocks the urethra. The

M. suburethralis penis and the dorsal tendon of the penis are well

developed. Burt (1960) illustrated this element of N. squamines in

part, the distal processes being omitted. The shaft is broad, and

slightly curved. Its base has two well-developed condyles and as

mentioned above, the distal processes are well developed. In the

specimen examined, the latter were not ossified.

A single pair of preputial glands is present, situated on the

lateral borders of the glans penis. These are long and narrow,

measuring 14 x 4 mm each. Each is drained by a single duct.

A pair of bulbo-urethral glands is situated in approximately the

same position as described for Sigmodon, though the median border of

each gland is in contact with the rectum in Nectomys. In the other

genera examined the gland is not located so deep. Each gland is

drained by a single duct that enters the dorso-lateral wall of the

membranous urethra anterior to the origin of the phallus.

The vesiculars are large and ventrally recurved. The gross

appearance is one of extreme lumpiness. Members of the pair are











asymmetrical with the median borders being more irregular. The greater

curve is grossly lobate, as opposed to the fine compound lobations

present in Mesocricetus. Each gland possesses a single duct that opens

into the cephalic end of the prostatic urethra adjacent to the ampulla.

The ampullary glands are compact and lie about the vas deferens.

They encompass an area about 4 x 3 x 2 mm. Numerous ducts drain each

gland.

Five pairs of prostates are present in Nectomys. There are two

elongate pairs of ventral prostates. The median pair lies directly

caudad of the bladder, the ducts entering the prostatic urethra through

the ventral wall posterior to the neck of the bladder. The lateral

pair is of the same size (9 x 3 mm), but is drained by ducts entering

the urethra lateral to the neck of the bladder. The median pair

remains white in FAA the lateral pair assumes a red color. A typical

pair of dorsal prostates lies at the anterior portion of the tract on

the dorsal surface of the prostatic urethra. The ducts from these

glands enter the urethra through the antero-dorsal wall. The bodies

of these glands encroach upon the dorsal surface of the vesiculars.

The colon passes between the two lobes of the glands. A smaller,

more lateral pair of glands is situated on the sides of the prostatic

urethra below the dorsal prostates. Their ducts seem, however, to open

into the prostatic urethra next to the ducts of the dorsal prostates.

Because of their general morphology (the tubules appear identical to

those of the dorsal prostates) and the proximity of the ducts, I

consider these glands to be a second dorsal set, though more laterally

located. Both sets of dorsal prostates are white in FAA. The filiform










anterior prostate glands lie in the lesser curve of the vesiculars.

Because of the great asymmetry of the vesiculars these prostates lie

on both lateral and median aspects of the vesiculars. Each gland is

drained by a pair of ducts entering the prostatic urethra close to the

duct of the vesicular.











Akodon Meyen 1833

(Fig. 40)

Hooper (1959) mentioned that the glans penis was of the complex

type, but did not elaborate further. The accessory circulatory
structures are small (Fig. 9). The penile blood sacs are the smallest

in any complex phallus I have examined. The distal architecture is

small (reduced?), and the accessory circulatory structures are corres-

pondingly reduced. The shaft of the baculum is laterally compressed

and almost bladelike (Fig. 11). The base is somewhat expanded. The

three digital processes are small, the median most ventral in position

and apparently partially blocking the urethra. The median process is

the largest, and all three processes are cartilaginous.

There are two pairs of preputials as in Sigmodon, a small

ventral pair (2 x 1 mm) and a larger lateral pair (5 x 3 mm). Each

gland is drained by a separate duct. The lateral pair has a flaring

proximal end and a ventral concavity in which lies the small pair.

The bulbo-urethral glands are in the same position as in Sipmodon,

each gland being drained by a single duct entering the dorso-lateral

wall of the membranous urethra anterior to the origin of the phallus.

The vesicular glands are small and recurved and slightly scalloped

along the greater curve. Each is drained by a single duct, which

enters the anterior wall of the prostatic urethra adjacent to the vas

deferens.

The paired ampullary glands do not differ in any fundamental way

from those of Sigmodon.











Three pairs of prostate glands are recognized in this genus. The

single pair of ventral prostate glands is median in position, the ducts

entering the prostatic urethra through the ventral wall posterior to

the bladder. The dorsal prostates lie somewhat anterior to the urethra,

encroaching upon the dorsal border of the vesiculars. Their ducts

enter the antero-dorsal wall of the urethra. The colon passes medially

between the two lobes. A single pair of anterior prostate glands is

present, although each has a bilobed appearance. One lobe runs craniad

along the lateral border of the corresponding vesicular. The second lobe

is a small rosette of prostatic tissue situated on the ventral border

of the vesicular prior to the entrance of that gland into the prostatic

urethra. The ducts of the two lobes of each side of the anterior

prostate glands are indistinguishable, however. All prostates were

white in preservative.

The specimen examined had small blotches of pigment in the tunica

which gave the testis a "polka-dot" appearance. Whether this pigment

pattern is characteristic of Akodon or simply an artifact is not

certain. The testis of the specimen studied was also slightly irregular

in outline, being depressed in several places by the epididymis.










Phyllotis Waterhouse 1873

(Fig. 41)

The phallus of Phyllotis is complex and the surface of the glans
is spined. Pearson (1958) illustrated the partially dissected glans

and the baculum of three species.

The preputial glands were not present on the specimen I examined.

However I had only a carcass remaining from a skin preparation, and it

is not certain that these glands had not been lost.

The paired bulbo-urethral glands lie in the same position described

for Signodon. The gland body is not pearshaped as in Sigfodon but is

concave on one side forming a "saucer-like" structure.

The vesiculars are large and ventrally recurved toward the rear.

The outer margin is slightly lumpy, while the lesser curve is smooth.

The duct arrangement is similar to that of Signodon.

The ampullary glands are well developed, the greatest mass of

the gland being concentrated on the dorsal aspect of the vas deferens.
Each gland is slightly bilobed.

There are four pairs of prostate glands. A bulbous, median pair

of ventral prostates lies caudad of the bladder. The ducts enter the

urethra through the dorsal wall posterior to the neck of the bladder,

the ducts following the neck into the prostatic urethra. A smaller,

lateral pair of ventral prostates lies along the neck of the bladder,

at which point the ducts enter the urethra. The dorsal prostates lie

on the dorsal wall of the prostatic urethra and partially encircle the

colon. The ducts enter the antero-dorsal wall of the prostatic urethra.

The paired anterior prostates lie in the lesser curve of the vesiculars.











Each enters the prostatic urethra at its anterior border by two ducts.

All prostates are white in preservative.

The testis is indented by the cauda epididymis. The corpus

epididymis is very narrow and almost indistinguishable. The vas

deferens exhibits no unique features.











Nyctomys De Saussure 1860

(Fig. 42)

The glans is covered by spines, which are small distally but
become larger at the proximal end. The spines at the proximal portion

are the largest in any genus in this study. The structure of the glans

penis is complex, although a reduction in the complexity is evident.

Thus the distal processes are small and almost lacking in cartilaginous

tissue. The circulatory tissues of the distal portion comprise most

of the mass. The penile blood sacs are not proportionally reduced.

Burt (1960) illustrated part of the baculum, but did not include the

digital processes. The base of the specimen I have examined is more

expanded than in Burt's illustration, though this may be due to the age

of the specimen.

No preputials were found in the specimen examined.

The paired bulbo-urethral glands are situated in the same position

as described for Sigmodon, although they are more ovate than in the

latter. A single duct drains each gland and enters the membranous

urethra anterior to the origin of the phallus.

No vesiculars were present in the specimen examined.

The ampullary glands are large, 5 x 5 mm, and are loosely filiform

in nature in contrast to the more compact type exhibited by Sigmodon and

some other genera. Each gland empties into its corresponding vas defer-

ens by numerous ducts prior to the formation of the ampulla.

Only a single pair of prostates are present in this genus, forming

the most anterior extension of the tract, and apparently represent the











anterior prostate series. On each side there are four units, each

drained by a single duct entering the antero-dorsal wall of the prostatic

urethra lateral and dorsal to the ampulla. These units are long and

thin (15 x 3 mm) and are composed of two to eight branching tubules.

The only other genus in which the prostates are similar to Nyctomys

to Neotoma, though Nyctomys lacks the ventral prostates which are

present in Neotoma. The phallus of Nyctomys is complex however,

while that of Neotoma is simple.

The testes are stubby and blunted at the ends in the specimen

available. There is little fat deposition about the epididymis. The

cauda epididymis does not cap the posterior pole of the testis as is

the usual case, but instead lies to one side and in contact with

the gonad.










Peromyscus Gloger 1841

(Fig. 43)

The phallus of Peromyscus has been the subject of a comprehensive

study by Hooper (1958) in which many species are described and figured.

The phallus is of a simple architecture with none of the additional

circulatory structures associated with the complex type of phallus.

The glans of some species bear spines. The specific variations in the

bacula of numerous species of Peromyscus have been described by a

number of different workers: Sprague (1939), Blair (1942), Clark (1953),

Hooper (1958), Tamsitt (1958), and Burt (1960). The baculum of this

genus is a simple rod-shaped structure, dorso-ventrally flattened with

a laterally expanded basal portion.

Preputial glands were not present in the specimen of this genus

examined.
The vesicular glands are large and recurved, measuring about 50 mm

along the greater curve. The margin of the greater curve is very
prominently notched, while the lesser curve is smooth. A single duct

drains each gland.

The ampullary glands lie along the vas deferens as they join

craniad to the neck of the bladder. The ventral aspect of the vas

deferens is not covered by ampullary tissue. The total area of the

glands is about 4 x 4 x 3 mm, a considerable portion of which lies on

the cranial border of the vas deferens.

Four pairs of prostate glands are distinguishable in the specimens.

A medial pair of ventral prostates is located directly caudad of the

bladder (8 x 5 mm). The second, lateral to the bladder, (10 x 7 mm) has










a concave ventral surface through which passes the vas deferens. The

ducts of both pairs of ventral prostates enter the ventral side of the

urethra. The dorsal prostate glands lie on the most antero-dorsal

portion of the prostatic region, abutting against the vesiculars. The

descending colon passes between the two lobes. The ducts enter the

dorsal aspect of the urethra. The anterior prostate glands are long

attenuate glands lying in the lesser curve of the vesiculars. They

measure 12 x 3 mm. Each gland is drained by two ducts that enter the

urethra lateral to, and in contact with, the vesicular ducts. All

prostates are while in preservative.

Both the caput and cauda epididymis are invested with yellowish-

green fat, and the corpus epididymis is very thin. The cauda epididymis

is attached to the testis by a mesentery but does not cap the posterior

pole of the testis as in Sigmodon.











Reithrodontomys Giglioli 1873

(Fig. 44)

The phallus of this genus has been figured by Hooper (1959).

The baculum Is a simple rod, expanded at the base, and has been

described for several species by Benson (1939), Blair (1942), Hooper

(1959), and Burt (1960).
Preputial glands could not be observed in the specimens

examined.

The horns of the recurved vesiculars are quite lumpy, curving

ventrally then folding back upon themselves. Along the greater curve

they may measure 15 mm. A single horn of the vesicular may contain

as many as eight lumpy protuberances. The ducts lie lateral and dorsal

to the vas deferens.

Each member of the paired ampullary glands lies in association with

the corresponding vas deferens to which it is adnate. They are located

craniad to the bladder in the region in which the vasa deferentia join.

The ampullary glands are compact and each covers the vas deferens with

which it is associated on all but the ventral surface.

There are four distinct pairs of prostates developed in this genus.

A bulbous (4 x 3 mm), median pair of ventral prostate glands lies

caudad to the bladder. This pair is white mhen fixed in FAA. Dorsal

and lateral to the median pair is a smaller (1 x 1 mm) set, which is

also white in FAA. The ducts of both of these pairs of glands enter

the ventral and lateral walls of the urethra. The dorsal prostates lie

on the dorsal and most anterior portion of prostatic urethra and are











separated by the colon. The gland, which is pink in FAA, drains into

the antero-dorsal portion of the urethra. One lobe measures 3 x 2 mm.

The anterior prostates are elongate (6 x 3 mm), lying in the lesser

curve of the vesicular, and draining, by two ducts on each side,

parallel to the ductus deferens and openings of the vesicular ducts.

The caput and cauda epididymis are invested with yellow fat.

The cauda epididymis is attached to, but does not cap, the posterior

pole of the testis.











Neotoma Say and Ord 1825

(Fig. 45)

The architecture of the phallus is simple; the glans is spined.

Hooper (1960) reviewed the glans penis in neotomine rodents and figured

this structure for N. floridana. The baculum is not constant within

the group, ranging from an elongate, gracefully curved structure as in

N. lepida to a small, almost triangular one in N. fuscipes. The

diversely shaped bone of this group has been described for numerous

species (Howell, 1926; Burt and Barkalov, 1942; Hoffmeister and de la

Torre, 1959; Hooper, 1960; and Burt, 1960).

The accessory glands have been figured by Howell (1926). Preputial

glands are not present in the members of this genus that I have examined.
Howell (1926) commented on a small sac-like structure in _. intermedia

that may have represented a vestigial preputial.

The bulbo-urethral glands are more flattened than is the case

for the other genera examined.
Vesicular glands are not present in the specimens of this

genus I have examined.

The ampullary glands are quite large and diffuse. Combined they

measure 15 x 10 mm, extending some 5 mm craniad of the anterior

extension of the vas deferens. There are numerous ducts from each lobe

of this gland entering the corresponding vas deferens for the final

5 7 mm of this organ.
There are two pairs of prostate glands. The ventral prostate

glands are long and narrow and the tubules are filiform. Each lobe











measures over 12 mm long, the widest is 6 mm. The ducts enter the

dorsal aspect of the urethra lateral to the neck of the bladder. A

very large and diffuse pair of anterior prostate glands is located

in the position usually occupied by the vesicular. The tubules are

heavily branched, assuming a fan-like appearance. The glands are

some 25 30 mm wide in greatest expanse. The tubules are widest

near the bladder, becoming more narrow as they continue to branch.

There are two ducts on each side entering the prostatic urethra lateral

to the ductus deferens.

Howell (1926) described and figured the accessory glands of

leotoma. The glands that are designated as "coagulating" by him

apparently are the ampullary glands, while those denoted as "vesicular"

represent one of the prostate series. According to my interpretation,

vesiculars are not present in this genus. The branched, filiform

nature of the glands in question is characteristic of the prostate

series.

It is not clear which of the prostate glands are represented by

the "vesiculars" of Howell. There is no typical dorsal prostate in

1leotoma. Thus, these fan-shaped glands could be either highly modified

anterior or dorsal prostates. I have referred them to the anterior

prostates for the following reasons:

1) The tubules of the dorsal prostates are generally of a smaller diameter

than the glands in question.

2) The ducts (two on each side) enter the prostatic urethra lateral to

the ductus deferens, as is the usual condition for the anterior prostates.










3) The fan-like nature of these glands can be more easily derived from
the usual condition of the anterior, rather than dorsal, prostates.

Most forms that possess a large anterior prostate also have a large,

recurved vesicular. It is within the lesser curve of these vesicular

glands that the anterior prostate usually lies. If the vesicular

glands drop out, the anterior prostate, with its filiform nature, would

probably expand, producing an effect similar to the condition found in

Neotoma.

The testes never become completely scrotal (Howell, 1926). The

cauda and caput epididymis are invested with yellow fat. The cauda

epididymis does not cap the posterior pole of the testis. The corpus

epididymis is very broad. The vas deferens is not convoluted at any

point. There is a gradual swelling of the vas deferens for about the

distal half of its length.











Tylomys Peters 1866

(Fig. 46)

Hooper (1960) described the glans penis of this genus. The

structure of the phallus is of the simple type, and the surface is

spined. The baculum in the two species described, T. fulviventer and

T. nudicaudus (Hooper, 1960; Burt, 1960), is a simple, rod-shaped

bone, expanded at the base and capped at the distal end by a carti-

laginous tip.

I cannot confirm the presence or absence of the preputial glands

in this genus as the specimen available to me was lacking the distal

portion.

The paired bulbo-urethral glands are similar to those in the

other forms examined.

The condition of the ampullary glands are the most distinctive

feature of the male tract of this genus. Each ampullary gland is

associated with a corresponding ampulla. The ducts, several from each

gland, enter the ampulla (Fig. 46, B) lateral to the entrance of the

vas deferens. The ampulla is the largest and most well developed of

any cricetid examined. It is bulbous, with the ampullary gland attached

laterally appearing as a diverticulum from the ampulla. The gland is

about 3 mm long, and folded upon itself. This condition is unlike

that found in any other cricetid genus examined in this study.
The vesicular glands are lumpy and irregular in shape. They are

not truly recurved in the manner of Sig~odon, but instead have the

anterior ends twisted and lying upon the main body of the gland.











There are only two pairs of prostate glands in this genus. A

small (5 x 3 mm), median, compact pair of ventral prostate glands is

located caudad of the bladder, the ducts entering the ventral wall of

the urethra just posterior to the neck of the bladder. A second, more

diffuse pair of prostate glands is situated at the anterior end of the

prostatic urethra on the dorsal border. These ducts enter the urethra

at this point. These glands are filiform as is often the case with the

anterior prostates, but occupy the position of the dorsal prostates of

the other genera. About 6 8 unconvoluted tubules constitute each

part of the gland. These are more easily seen and dissected in a

specimen that has not reached full sexual development, than in an adult,

as in the latter, they are too distended and associated with much fatty

tissue.

The testes are large, 26 x 15 mm, in the slightly desiccated

specimen available, and the cauda epididymis lies to one side of the

testis (Fig. 46, C) rather than capping the posterior pole. The cauda

and caput epididymis are lumpy and irregular on their surfaces, the

latter being invested with yellowish fat.











Balomys True 1894

(Fig. 47)

Hooper (1959) figured the phallus of B. musculus. The plan of

the glans is simple, and the surface is spined. The baculum is short,

irregularly expanded at the base and faintly forked at the distal end.

This element has been figured for B. musculus by Hooper (1959) and

Burt (1960). The latter illustrates two specimens that are quite unlike.

Hooper's illustration is different still. The baculum is either extremely

variable in this genus or some other explanation must be afforded for

the discrepancies between the published accounts of this element.

Blair (1942) described this element in B. taylori.

A single pair of preputials is located on the sides of the

glans. They are small (5 x 2 mm), expanded proximally, and drained by

a single duct on each side.

The vesicular glands of Baiomys are quite simple and small

(8 x 1.5 mm). They are straight for most of their length, and recurved

only at the tip.

The ampullary glands are the most reduced of any genus studied.

They consist of four to six simple tubular glands draining directly into

the corresponding vas deferens. The individual tubular elements are

not connected. They are very small, being less than 1 mm in length.

Paired ventral, dorsal, and anterior prostates are present. The

former are located posterior to the bladder and measure 4 x 3 mm.

Their ducts enter the ventral wall of the prostatic urethra caudad

of the neck of the bladder. The dorsal prostate glands lie on the

anterior cephalic border of the prostatic urethra, the descending colon











passing between the two lobes of the gland. The ducts enter the dorsal

vall of the prostatic urethra. The anterior prostates lie at the cephalic

end of the urethra and extend along the border of the vesiculars but are

not adnate thereupon. They are about 4 mm long, and filiform in appear-

ance. All prostates are white in FAA.

The testis appears almost spherical (4 x 3 mm), and the cauda

epididymis which caps the posterior pole is large and invested with

greenish-yellow fat.










Ochrotomys Osgood 1909

(Fig. 48)

The glans penis (Fig. 8) is of the simple type (Hooper, 1958).

The glans is spined, these appearing somewhat larger than Hooper's

description of them as "minute." The distinctiveness of the glans

penis-together with dental and certain other characteristics prompted

the recognition of the generic status of Ochrotomys whereas it had

previously been considered as a subgenus of Peromyscus (Hooper, 1958).

The baculum is a small, blunt rod with a laterally expanded basal

portion. The bone has been figured by Hooper (1958) and Burt (1960).

A pair of preputial glands is present, lying on the sides of the

glans penis. They are small, about 4 x 1 mm, a single duct draining

each of these glands.

Ochrotomys is characterized by small vesicular glands which

appear as simple tubular structures. They are about 10 x 2 mm and

slightly recurred near the tip. The recurving appears to follow no

consistent pattern.

No ampullary glands could be demonstrated in dissection.

Four pairs of prostate glands can be recognized. A single median
pair of ventral prostate glands lies posterior to the bladder. These

are small and bulbous. A second pair, loosely divided into two lobes

on each side is situated lateral to the neck of the bladder. The

ducts of the two sets enter the urethra on the dorsal aspect, posterior

and lateral to the bladder respectively. Both sets are white in FAA.

The dorsal prostate glands are small and lie at the anterior end of the

urethra on the dorsal side. The pair cradles the descending colon. The

ducts enter the prostatic urethra dorsally.

58










The anterior prostate glands lie at the base of the vesiculars and

enter the prostatic urethra by what appears to be a single duct from

each side, situated next to the vas deferens. Since the vesiculars are

reduced in size these glands have a more compact nature than in those

forms which have a large vesicular upon which to spread. From the median

pair of ventral prostates to the dorsal prostate there is but a mass of

prostatic tissue broken into the units previously described. Of all

forms described, this one has the most poorly defined sets of prostates.

The anterior prostate is not typical, but the ducts are in the proper

position. There appears to be but one duct from each member of the pair,

whereas most other genera examined have two.

The testis is relatively large (11 x 6 mm). The cauda epididymis

caps the posterior pole of the testis. The epididymis is invested with

yellowish-green fat. The vas deferens is slightly convoluted throughout

its length.










Onychomys Baird 1857

(Fig. 49)

The phallus which has been figured by Hooper (1959), is of the

simple type and the glans is spined. Hooper (1959) illustrated 0.

torridus, but commented that leucogaster was similar, differing only

in proportions. The bacula of both species have been described and

figured by Burt (1960), and Hooper (1959) illustrated 0. torridus.

"It is a short bone with a round knob for a base, and with a laterally

flattened shaft" Burt (1960).

A pair of preputial glands lie on the lateral sides of the glans

penis, the ducts opening near the distal end of the prepuce. These glands

are long and narrow (8 x 2 mm).

The bulbo-urethral glands are large (4 x 3 mm) in this genus but

otherwise similar to those of Sigmodon.

The male genital tract of Onychomys is distinctive in that both

vesicular and ampullary glands are absent. Neither vesicular nor

ampullary glands were seen in the specimen examined.

The genus possesses two pairs of prostate glands. A single

median pair of bulbous (4 x 3 mm) ventral prostates are present. These

are white when preserved in FAA. The ducts enter the urethra on the

ventral surface lateral to the neck of the bladder. A median inflated
(4 x 3 mm) pair of dorsal prostate glands is located at the anterior

portion of the prostatic urethra in the position usually occupied by the

absent vesicular. The lobes are not separated by the colony The ducts

enter the urethra dorsal to the vas deferens.

The testis appears long and narrow (11 x 5 mm). The cauda epididymis
caps the posterior pole of the testis, and tapers to form a cone with a











rounded tip. The vas deferens is heavily convoluted throughout its

length, a condition not observed in any other genus examined.











Synaptomys Baird 1857

(Fig. 50)

The phallus is of a complex nature, the surface of the glans is

spined. The structure of the glans penis of this or any other microtine

does not seem to differ from that of Sifmodon. All accessory circu-

latory structures recognized in Sigmodon are present. The baculum of

this genus was first figured by Hibbard and Rinker (1912) for S. cooper.

Hamilton (1946) demonstrated the trifurcate nature of this element,

not noted in the previous work. Dearden (1958), Burt (1960) and Ander-

son (1960) have all figured this element and discussed its structure.

A single pair of preputials is present and are proportionally the

largest in any genus examined, spreading out upon the M. rectus abdominis

from their origin in the tissues of the prepuce. They were 15 x 10 mm

in an adult specimen and are drained by a single duct on either side of

the glans penis. The broad flaring preputials are a particularly
striking feature of the male tract of Synaptomys, even for the microtines,

where preputials average proportionally larger than those of any other

group examined.

The vesicular glands are well developed and of a simple tubular

nature, They are irregular in diameter, and lumpy at certain points,

though the general appearance is not one of extreme irregularity. They

are convoluted at the ends, though the convolutions do not seem to

follow any particular pattern. One measures 15 x 3 mm when straightened.

The vesiculars empty into the prostatic urethra adjacent to the vas

deferens by means of a single duct from each gland.











The ampullary glands are small, tightly knit glands lying adnate

to their corresponding vas deferens into which they are drained by

numerous ducts. Each ampullary gland appears to contain about eight

compound bulbous units, tightly bound about the vas deferens.

Four pairs of prostate glands are recognized. One major pair of

ventral prostates lies slightly posterior and lateral to the neck of

the bladder. These are elongate (8 x 4 mm). A second smaller pair of

ventral prostates is present at the base of the preceding, though the

ducts are located slightly closer to the lateral border of the neck

of the bladder. These two sets of glands are not as clearly distinct

as those of some other genera. Both are white in FAA. The ducts of

both sets pass through the ventral wall of the prostatic urethra, poster-

ior and lateral to the neck of the bladder. The dorsal prostates are

large (8 x 3 mm), situated on the antero-dorsal border of the prostatic

urethra, and extend somewhat cephalic of this structure. The colon

passes between the lobes of this paired gland. The ducts enter the

antero-dorsal wall of the prostatic urethra. The anterior prostates are

attenuate glands lying adnate to the dorsal border of the vesiculars for

about 8 mm. They do not closely resemble the anterior prostates of some

of the cricetids such as Signodon or some other microtines such as

Ondatra. The ducts, two on each side, enter the anterior wall of the

prostatic urethra ventral and lateral to the ducts of the vesicular

glands.

The testis is rather small (7 x 5 mm), capped at the posterior

pole by the cauda epididymis. The whole of the epididymis, especially

the caput, is invested with greenish-yellow fat.










Ondatra Link 1795

(Fig. 51)

The glans penis is complex and the surface spined. The arrange-

ment of accessory circulatory structures is similar to that described

for Signodon. The penile blood sacs are well developed, as are the

tendons and muscular components of the phallus. As the largest of

cricetid rodents, the parts of the phallus are considerably larger, and

more developed than in smaller forms, though not disproportionately.

The baculum has been figured by Hamilton (1946), Didier (1954), and

Burt (1960). Anderson (1960) described, but did not figure this bone:

he commented that Hamilton's interpretation of dorsal and ventral was

not correct. The element is the largest trident-shaped bone seen. All

digital processes are somewhat spatulate, with an uneven border. The

median process is deflected ventrally, and a small keel is present

separating the lappet tips of the urethra in the flaccid condition.

The large, paired preputial glands spread across the M. rectus

abdominis to a considerable extent. The largest measured wore almost

50 mm long x 10 mm wide. Each gland is drained by single duct lying on
the dorsal aspect of the glans penis.

The large, heavily convoluted, tubular vesicular glands are very

irregular. There is no apparent pattern to the twisting and turning,

other than accomodation to the other organs of the abdominal cavity.

There is moderate branching and location, but the general simple tubular

nature of the glands is not obscured. Straightened, a single vesicular

may measure as much as 75 mm. For comparison a human vesicular measures

about 100 mm (Weyrasch, 1959). Each gland drains through the anterior










wall of the prostatic urethra by means of a single duct that lies dorsal

and lateral to the ampulla.

The ampullary glands are attached to the vas deferens, draining

into it by means of numerous ducts at the point at which the vas deferens

enters the ampulla. The total area of these glands is approximately

15 x 10 x 5 mm. Three ventral and four dorsal lobes can be distinguished
in each gland.

There are four pairs of prostates. An elongate (20 x 10 mm)

pair of median ventral prostate glands lies posterior to the bladder.

The ducts enter the ventral wall of the prostatic urethra directly

caudad of the neck of the bladder. These glands are white in FAA. A

smaller (5 x 4 mm), more bulbous and lateral pair of ventral prostate

glands that is purple in FAA lies at the base of the larger glands.

The ducts enter the urethra near the neck of the bladder. The dorsal

prostates are large (15 x 10 mm) glands lying on each side of the

colon and on the antero-dorsal border of the prostatic urethra. A

large, 25 x 8 mm, pair of anterior prostate glands lies upon the

ventro-lateral surfaces of the vesiculars. Each opens into the prostatic

urethra by four ducts that lie next to the vesicular ducts.

The testis is large (25 x 12 mm), the cauda epididymis lying at

the posterior pole, but not "capping" it. The epididymis is invested

with yellowish fat. The vas deferens is unconvoluted.










Neofiber True 1884

(Fig. 53)

The phallus is of the complex type, the surface of the glans

penis being spined. The internal structure of the glans is very

similar to that of Sigmodon (Fig. 8). The baculun was described by

Hamilton (1946) and Anderson (1960). The median process of the baculum

is not ossified in young specimens, but in some older individuals this

ossification does occur. Whether the ossification center occurs in all

individuals is, however, questionable.

A large pair of preputial glands is present. They cover part of

the M. rectus abdominis. They are proximally expanded, measuring 20 x

10 mm. Each gland is drained by a single duct that lies on the lateral

aspect of the glans penis.

The vesicular glands are large, convoluted tubular glands that

measure as much as 50 mm when straightened. They are fairly uniform

(about 5 7 mm) in thickness. The convolutions are either medial or

lateral, and appear to have no constant pattern. Each vesicular gland

is drained by a single duct which opens into the prostatic urethra

adjacent to the vas deferens.

The ampullary glands partially surround the vas deferens, anterior

to the neck of the bladder. Each gland is associated with its corres-

ponding vas deferens, into which enter numerous ducts. These glands,

like the corresponding ones in Ondatra are divided into several lobes

which are tightly bound together.

Three sets of prostate glands can be recognized. A very large

pair of ventral prostates is located directly posterior to the bladder.

66











These glands measure 18 z 11 mm in length and width in one adult

individual. This pair of glands may be teased apart into two lobes on

either side. However, since there seems to be but one duct system

entering the prostatic urethra, posterior and slightly lateral to the

neck of the bladder, it is assumed that only one pair of glands is

represented. A single pair of dorsal prostates are present, located on

the antero-dorsal wall of the urethra, the colon passing between the

two lobes. A single gland measured 11 x 5 mm in length and width. The

ducts enter the urethra through the antero-dorsal wall. The paired

anterior prostate glands lie on either the lateral, dorsal, or ventral

borders of the vesiculars, and are drained by four ducts on each side.

The ducts enter the prostatic region lateral to the ducts of the

vesicular glands. In one specimen, I had difficulty separating these

from the dorsal prostates to which they were bound with connective

tissue. This emphasizes the importance of examination of duct systems

rather than masses of glandular tissue in distinguishing between these

various prostatic units.










Microtus Schrank 1798

(Fig. 53)
The structure of the phallus is of the complex type and the
surface of the glans is spined. I have not examined the architecture of
the glans in detail, but it does not seem to differ from that of
Neofiber (Fig. 8) in any appreciable manner. The baculum of the follow-
ing species of Microtus have been described or figured: M. agrestris
(Ognev, 1950; Anderson, 1960), M. arvalis (Ognev, 1950; Didier, 1954;
Anderson, 1960), M. californicus (Anderson, 1960; Burt, 1960), M.
chrotorrhinus (Hamilton, 1946), M. fortis (Ognev, 1950; Anderson, 1960),
}. gregalis (Ognev, 1950; Anderson, 1960), M_. guatemalensis (Anderson,
1960), M. guentheri (Anderson, 1960), M. longicaudus (Anderson, 1960;
Burt, 1960), M. mexicanus (Anderson, 1960; Burt, 1960), M4. miurus
(Anderson, 1960), M. montanus (Anderson, 1960), M4. nivalis (Didier,

1954; Anderson, 1960), Mf. oeconomus (Ognev, 1950; Anderson, 1960; Burt,
1960), 14. oregoni (Anderson, 1960), 1M. orcadensis (Anderson, 1960),
E_. pennsylvanicus (Hamilton, 1946; Dearden, 1958; Anderson, 1960;
Burt, 1960), M. richardsoni (Anderson, 1960), M. socialis (Argyropulo,

1933; Didier, 1954), and M. townsendii (Anderson, 1960). Hamilton
(1946) vas the first to note the presence of the proximal flaring of
the median process, and the keel ("spur") of that element.

Sough the tract was described by Hamilton (1946), my interpretation
of some of the structures does not coincide with his.
A single pair of preputial glands is present, lying on the lateral
sides of the glans penis. A single duct drains each gland. As










Hamilton (1941) states, these are small as compared to those of

Synaptomys and Clethrionomys.

The recurved vesicular glands are not unlike those of Clethrionomys

or Sigmodon, though they are smaller. The greater curvature is lumpy,

the lesser more smooth. Each gland drains into the prostatic urethra

by means of a single duct that courses dorsal and lateral to the vas

deferens.

The paired ampullary glands lie upon the vas deferens at the

point at which the latter converge, bend, and enter the urethra. Each

gland is associated with its corresponding vas deferens. The glands here

considered to represent the ampullary glands are evidently the "ventral

lobes" of the prostate of Hamilton (1941).

Four pairs of prostate glands are recognized in Microtus.

A median, somewhat elongate (6 x 3 mm) pair of ventral prostate glands

lies posterior to the bladder. A second, more bulbous (4 x 3 mm)

pair of ventral prostates is situated more laterally. The ducts of the

median pair enter the prostatic urethra posterior to the neck of the.

bladder, those of the lateral pair enter the urethra near the sides of

this structure. Hamilton (1941) did not mention these glands, though

they appear in his illustration. The paired dorsal prostate glands

lie along the anterior cranial border of the prostatic urethra. The

anterior margins of these glands sometimes encroach upon the dorsal

border of the vesicular gland on the corresponding side. The ducts

enter the urethra through the antero-dorsal wall, under the main body

of the gland. Hamilton (1941) did not discuss these glands, though

they are visible in his dorsal view of the tract. The paired anterior











prostate glands lie in the lesser curves of the vesicular glands,

along the lateral borders. They are drained by two ducts on each side

which enter the urethra adjacent to the ducts of the vesicular glands.

These are the "ventro-lateral lobes of the prostate" of Hamilton

(1941).

The testis, epididymis, and vas deferens are usual in all

regards, and are adequately described by Hamilton (1941). He comments

upon the large amount of yellow fat at the caput epididymis, mentioning

that it may be glandular.










Pedomys Baird 1857

(Fig. 54)

I have not examined the glans in detail, but it does not appear

to differ from that in Microtus (sensu strict) in any appreciable

manner. The baculum has been described by Hibbard and Rinker (1943),

Hamilton (1946), Burt (1960), and Anderson (1960).

The preputial glands lie on the sides of the glans penis. In

the specimen examined they were small (5 x 2 mm), although I am not

certain that this represents maximum development. Usually the

preputials of the Microtinae are very well developed.

The simple tubular vesicular glands are irregular, lumpy, and seem

to represent an intermediate condition between the recurved and con-

voluted types. They are slightly recurved at the terminal portion.

A single gland, when straightened, measured 12 x 3 mm. A single duct

drains each vesicular gland.

There is little glandular tissue of the ampullary glands on the

ventral surface of the vas deferens, most of it being concentrated on

the cephalic, dorsal, and caudal aspects.

There are four pairs of prostate glands. A median, bulbous pair

of ventral prostate glands is situated caudad to the bladder, the ducts

entering the ventral wall of the prostatic urethra at this point. Each

member of the pair is composed of two lobes (a total of four lobes in

this caudad of the bladder). The ducts are confluent, and the nature of

the tubules of the glands is identical. I, therefore, recognize only a

single set of glands in this position. A second, more lateral pair of

ventral prostate glands is located alongside the neck of the bladder,











the ducts entering the prostatic urethra lateral to the neck of the

bladder. All ventral prostates are white in FAA and formalin. The

dorsal prostate glands lie at the antero-dorsal border of the prostatic

urethra, their cephalic edges encroaching upon the dorsal aspect of the

vesicular glands. The ducts of these prostates enter the dorsal vall of

the urethra. The colon passes between these paired glands. The
anterior prostate glands lie along the ventral and lateral aspects of

the vesicular glands. Each gland is loosely bilobed, the longest lobe

(7 x 2 mm) being situated dorsally and projecting more cephalically.
The smaller (3 x 1 mm) is ventral to the larger. These glands empty

into the urethra by means of two ducts on each side (one from each lobe).

which lie adjacent to the ducts of the vesicular glands.
The testis of the specimen examined is small (12 x 7 mm), the

cauda epididymis lying adjacent to the posterior pole. All parts of

the epididymis are invested with yellow fat.










Pitymys McMurtrie 1831

(Fig. 55)

The glans penis of this genus, although not examined in detail,

does not appear to differ from that of Neofiber or Sigmodon in any

salient manner. The bacula of the following species have been described:

P. Pinetorum (Hamilton, 1946; Anderson, 1970; Burt, 1960), P. pyrenaicus

(Didier, 1954), P. quasiator (Anderson, 1960; Burt, 1960), .. fatioi

and arr lus (Anderson, 1960). Judging from the comments and

illustrations of these authors, considerable inter- and intraspecific

variation occurs in the baculum of this genus.

The preputial glands lie on the sides of the glans penis and are

drained by a single duct on each side. These glands encroach slightly

upon the M. rectus abdominis.

The vesicular glands are large and irregular. They cannot be

described as either convoluted or recurred. The terminal portion is

lobate. A single gland measures 10 x 4 mm. The terminal lobes are

depressed ventrally, but do not then curve posteriorly. Each gland is

drained by a single duct that enters the prostate adjacent to the vas

deferens.

The ampullary glands lie in the usual position at the junction

of the vasa deferentia and each is adnate to its corresponding vas

deferens. The glands are divided into two major portions, lying massed

on the cephalic and caudal aspects of the vas deferens. There appear

to be several ducts associated with each ampullary gland.

There are four pairs of prostate glands. A median, bulbous

(4 x 4 mm) pair of ventral prostates lies caudad of the bladder, the











ducts entering the ventral wall of the urethra posterior to the neck of

the bladder. A second, smaller pair of glands (2 x 1 mm) lies lateral

to the neck of the bladder, their ducts entering the prostatic urethra

at this point. All ventral prostates are white in FAA and formalin.

These paired dorsal prostate glands lie at the antero-dorsal border

of the prostatic urethra, their cephalic edges extending upon the dorsal

aspect of the vesicular glands. The ducts of these prostates enter the

hntero-dorsal wall of the urethra. The anterior prostate glands lie

on the ventral border of the vesicular glands. They are drained by a

pair of ducts on each side which enter the urethra adjacent to the

ducts of the vesicular glands.











Clethrionomys Tilesius 1850

(Fig. 56)
I have not examined the internal structure of the phallus of

this in detail, but it does not seem to differ from the typical com-

plex pattern, The trident-shaped baculum of this genus was figured

by Hamilton (1946). He noted the keel on the ventral surface of the

median process (he referred to this as the dorsal surface) that sepa-

rates the lappet tips of the urethra, though he did not mention its

relation to this structure. Burt (1960) figured this element, but

did not observe the keel ("spur" of Hamilton and Burt). The bacula of

the following species have been figured: C. glareolus (Ognev, 1950;

Didier, 1954), _. rutilus (Ognev, 1950; Anderson, 1960), rufocanus,

S, gapDeeri C. occidentalis (Anderson, 1960).
The vesiculars are large, recurved glands, irregular and somewhat

lobate along the greater curve. The inner margins are heavily lobate

(Fig. 56, B). They are drained by a single duct from each gland that

enters the anterior border of the prostatic urethra adjacent to the vas

deferens. Of the microtines examined, Clethrionomys has the most

heavily recurved vesicular glands. This genus, coupled with Microtus,

stands in marked contrast to other microtines with large convoluted

vesicular glands, though in other details of the tract all microtines

seem constant.

The ampullary glands surround the vas deferens, opening into the

latter through a number of ducts prior to the ampulla. In the specimens

examined these glands had a dark purple color. The original preservative











is not known and whether the color is an artifact or not is uncertain.

Clethrionomys is the only form studied in which the ampullary glands

were such a deep color in preservative. In some of the other genera,

these organs were a pinkish color, but never a deep purple. It is

interesting to note that the lateral pair of ventral prostates had

color identical to that of the ampullaries. A secretary similarity is

possibly suggested by this.

Four pairs of prostates are recognized. A small, 3 x 5 mm,

bulbous, median pair of ventral prostates lies directly posterior to

the bladder. These glands are white in the preservative. The ducts

from these enter the ventral wall of the prostatic urethra posterior

to the neck of the bladder. A second, more elongate (10 x 4 mm) pair

of ventral prostates, more irregular than illustrated, lies lateral

to the bladder. The ducts of these glands enter the prostatic urethra

lateral to the neck of the bladder. These are the same purple color

as the ampullary glands. A large, leaflike pair of dorsal prostate

glands (8 x 5 mm), lies on the antero-dorsal border of the prostatic

urethra through which the ducts of this gland pass at that point. The

colon passes between the two lobes of this gland. The anterior prostates

lie in the lesser curve of the vesiculars, either laterally or medially

depending on the nature of the recurring of the corresponding vesicular

gland. Each anterior prostate gland is drained by two ducts that enter

the prostatic urethra ventral and lateral to the vesicular ducts.

The testis measures 13 x 8 mm. The cauda epididymis almost "caps"

the posterior pole of the gonad, but lies a bit to one side. The tunica

of the testis is very thin, the seminiferous tubules being readily











visible. The testis is pushed in by both cauda and caput epididymis,

possibly because the tunica is so thin. The entire epididymis is

invested with greenish fat.











Rattus Frisch 1775

(Fig. 57)

The phallus is of the complex type and the surface of the glans

is spined. All of the accessory circulatory structures described for

Sigmodon are present. The nature of the glans penis, its apparent

functional morphology, and accessory structures does not seem to differ

in any significant manner from that of cricetids possessing a complex

phallus (Fig. 10). Greene (1935) discusses the origin of the phallus

as well as its innervation and circulation. The most comprehensive

osteogenic work on the baculum of any mammal was done by Ruth (1934)

on Rattus, Although this work is quite comprehensive concerning the

embryology of the shaft, the distal processes are scarcely considered

and no observations were made on the definitive morphology of the

bone. Greene (1935) figures the bone in association with nerves and

blood vessels of the penis, but does not mention the penile blood sacs

and associated circulatory structures.

The accessory glands have been well studied in Rattus, as would

be expected in an animal so frequently used in experimental research.

The majority of the work on this species has been concerned with the

effect of removal of certain prostate lobes, or effects of hormone treat-

ments. Walker (1910) described the anterior prostates as "coagulating

glands," and disclaimed any connection between these and other prostates

(p. 19). Price (1936) considered these glands to be members of the

prostatic series, as do most modern workers, although the name "coagu-

lating gland" is still frequently applied. Snell (1941) discussing

Mus, points out the prostatic nature of these glands.










All accessory glands have been figured, grossly and histologically,

and the ducts of each gland described by Price (1936), and previously
by Walker (1910), in part. Further description is unnecessary. I

recognize an additional pair of prostates probably of the ventral

series, based on vhat appears to be a separate duct system.

The same possibilities of a higher occurrence of morphological

aberrations in inbred strains of Rattus was discussed under Mesocricetus.











Mus Linnaeus 1758

(Fig. 58)

A very adequate gross description and histology of the male

genitalia of Mus is given by Snell (1941). The only discrepancy

between my observations and those previously reported is that I

recognize two pairs of ventral prostates (as I do for Rattus) where

Snell and others note only one. The phallus is of the complex type,

but it has not been studied in detail.

The same conditions of possible morphological aberrations

produced by inbreeding exist in Mus as discussed for Mesocricetus.














DISCUSSION


The Use of Genital Structures as Taxonomic Criteria


In any taxonomic study one comes to a point at which various

characters must be weighed as to their fundamental or superficial

nature. It would be useless to claim that genital morphology is more

stable per se than cranial or dental morphology which furnish many of

the criteria used in mammalian taxonomy. Indeed, it has many drawbacks.

The genitalia are more difficult to work with than are teeth, and

their nature does not allow definitive measurements to be made. There

is the further difficulty due to age and seasonal variation. Suitable

characters (i.e., ovarian histology ani placentation) may exist in the

females, but are not necessarily comparable to the characters known in

the males. An additional problem is the lack of fluid-preserved

specimens in most museum collections. Soft parts of most mammals,

other than our most common native forms, are difficult to obtain.

A difficulty inherent in the usage of the anatomy soft parts for

taxonomic criteria, is well stated by Vood and Patterson (1959):

". . the evidence of structures that there is, and presumably always

will be, no actual evidence of evolutionary sequence. ."

Any classification based on soft parts may thus be contrary to

the fossil record. This is a problem which can only be solved by more

comparative anatomical studies, dealing with both soft and hard parts,

until some compromise is reached.

81











Mossman (1953) has pointed out that the degree of plasticity in

any set of structures would theoretically be proportional to the degree

to which those structures interact with the environment. Of all

characters used in mammalian taxonomy, none interact with the environ-

ment more closely than the teeth. Every environmental shift could

presumably bring about some change in diet that might be accompanied

by different selective pressures on the dentition. Then, too, the

degree of convergence and parallelism that is known to exist in some

mammalian groups, as is the case with the rodents (Simpson, 1945;

Wood, 1950; 1955) leads one to be cautious of classifications based

solely on dental patterns.

It is difficult to see how the genitalia could be influenced

to any great extent by environment, though there may be some association.

The best statement of the supposed conservative nature of the genitalia

was made by Mossman (1953), in a discussion of the fetal membranes,

which is also perfectly applical to genital characters in general:

What then should one expect of the evolution of an organ
system, such as the fetal membranes, largely isolated
from the external environment and charged with a highly
complex job to do, but one which is fundamentally the
same in all members of the group, in this case the
Subclass Eutheria? It seems that, regardless of rate of
genetic variation of the system, divergence would be
relatively slow and narrow, and that intergradation would
be the rule, there being slight environmental selection,
and little race isolation due directly to adaptive
variations in this system itself. But while this type
of evolution would be taking place in an environmentally
independent organ system, the group of organisms in which
the organ system existed could nevertheless be undergoing
the usual evolutionary course in its other organ systems:
diverging widely in adaptation to environmental niches
old and new; losing species or whole major groups by
extinction; in short, becoming the widely divergent,
often aberrant or isolated groups that are characteristic
of mammals at the present time.

82










Despite such considerations, one must also consider that the

large number of phallic forms, especially the great variation found

in those of the simple type (Hooper, 1958, 1959, 1960), must be the

result of selective forces, either direct or indirect. To what degree

this is comparable to the selective forces operating on dental or

osteological characters is, of course, unknown.

It is unfortunate that so little information is available on

the embryology of many of the reproductive characters Until such

information is obtained, many of the homologies of various prostatic

series cannot be determined with assurance.

Of great concern in the taxonomic evaluation of the genital

characters discussed here, is a consideration of what degree of

genetic divergence is necessary to produce different glandular comple-

ments, and to what degree minor deletions of these complements affect

the animal in question. Thus, if the secretary role of a particular

prostatic pair is either dispensable, or can be carried out by another

pair of glands (prostatic or otherwise), any mutation producing the

reduction, or elimination, of the glands in question would not be

strongly selected against. As was previously mentioned, inbred

strains of Rattus and Mesocricetus do demonstrate aberrant character-

istics, showing, perhaps, that in certain populations genital variants

may become established.

Until much more information on the embryology, secretary nature,

and genetics of such characters is available, it is best to consider

genital characters as potential taxonomic characters in certain groups,

but certainly of no proven stability or freedom from selection.










Patterns of Morphological Variations in the Male
Genital Tract of Muroid Rodents


Structure of the phallus.-Two types of phallic structures,

simple and complex, are clearly evident among muroid rodents. Such

fundamental diversity as exists between these two types of glans

is of an impressive nature.

The complex form of phallus appears to be too intricate a

structure, and too similar in the various forms possessing it, to have

been evolved independently in various phyletic lines (Figs. 6, 8, 9,

and 11). It must therefore represent a fundamental pattern,

characteristic of both miuid and cricetid rodents, perhaps even the

Myomorpha. The simple type phallus, occurring in New World forms

only, would appear to be derived from the complex form in the

following manner: (1) reduction in the complexity of accessory circu-

latory structures and elongation of the shaft of the baculum. This

would have to be accompanied by a functional change as outlined on

page 14, resulting in the functional natures of the two types of

phalli; and (2) simplification and final elimination of the digital

processes of the distal end of the baculum. As the digital processes

are movable in the well developed complex phallus, and dependent

upon the accessory circulatory structures for this movement, their

regression following a loss of the latter structures would seem inevi-

table. The manner of formation of the dorsal vein of the penis in forms

possessing a simple type phallus (Figs. 9 and 10) seems to have retained

the nature of that of the complex type, though the penile blood sacs,

present in the primitive phallus, are not present.











Two genera, Akodon (Fig. 9) and Nyctomys, represent possible

stages in this development. In both genera the conditions for

reduction are met. This is not to say that these genera are ancestral

to certain modern genera with simple phalli, but that they demonstrate

possible stages in the development of the simple type. They may be

ancestral, or they may represent separate lines paralleling those

which have already developed the simple type of phallus.

Accessory glands.-The evidence of two distinct lines is not as

clear from the accessory glandular structures as from the phalli.

Certain genera of each of the two phallic forms have lost particular

series of glands. If the nature of the phallus is taken to represent

familial or subfamilial distinction, the accessory glandular complement

would logically be subordinate to this level, possibly at the tribal or

supergeneric rank. Here, one must weigh the frequency with which a

particular set of glands is lost or highly modified. If one gland set

has been dropped several times by several groups of animals, it would

appear to be of a less fundamental nature from a taxonomic standpoint,

than a gland set that has been retained by all but one group.

The preputial glands have been lost by numerous genera (Table 2),

some with a complex phallus, some with a simple phallus. Lack of

preputial glands is generally associated with the simple type phallus.

This is true of Peromyscus, Reithrodontomys, and Neotoma, but three

genera, Ochrotomys. Onychomys, and Baiomys. have both a simple phallus

and preputial glands. I have not examined the other six genera with

simple types of phalli listed by Hooper (1960). In the seven genera of

microtines examined preputials were large and conspicuous. No forms










TABLE 2

SUMMARY OF THE VARIATION IN ACCESSORY GLANDS


OF 24 MUROID GENERA


Genera


Mesocricetus

Sigmodon

Akodon

Oryzomys

Oecomys

Nectomys

Phyllotis

Nyctomys

Neotoma

Tylomys

Peromyscus

Reithrodontoiys

Baiomys


Phallus Preputial Bulbo-Urethral Ampullary Vesicular


Prostates (Pairs)
Dorsal Ventral Anterior

1 1 1

1 2 1


1

1

1

1

1

1-4?

1-4?

0

1

1

1


Phallus: C = complex type
S = simple type


X = structure present
0 = structure absent


* = 2 pairs present










TABLE 2-Continued


Genera


Ochrotomys

Onychomys

Synaptomys

Ondatra

Neofiber
CO
Microtus

Pitymys

Pedomys

Clethrionomys

Rattus

Mus


Phallus Preputial Bulbo-Urethral Ampullary Vesicular


Prostates (Pairs)
Dorsal Ventral Anterior

1 2 1











examined demonstrated as high a development of these glands as did the

microtines. Of the cricetines with a complex phallus type, only

Mesocricetus lacked preputial glands. The status of Phyllotis and

Tylomys in this respect could not be determined because of incomplete

specimens. Two genera, Akodon and Sigmodon, have two pairs of pre-

putial glands, a small ventral and a large lateral pair.

The bulbo-urethral glands exhibit the greatest uniformity of all

accessory glands. With but minor variations these glands occupy the

same position and have similar duct systems in all genera. These are

the most stable accessory glands in the reproductive tract of muroids,

possibly of mammals in general.

With the exception of Nyctomys, all genera with a complex phallus

had vesicular glands. Of the genera with simple phalli, only Neotoma

and Onychomys lack vesiculars. Baiomys and Onychomys have vesiculars

that are reduced. Only Peromyscus and Reithrodontomys of the genera

with a simple phallus type had well-developed vesicular glands.

The fully developed vesicular glands are quite large in most

genera. They are easily the largest glands of the tract. Basically

the vesiculars are simple tubular glands, though when distended they

become thrown into numerous convolutions. These may be of two basic

types. In cricetines and muroids, they become recurved, and highly

irregular on the greater curve of the gland. In microtines, and those

cricetines in which the glands are reduced, the tubular nature of the

glands remain apparent, and numerous bends, apparently fortuitous, are

made. In these particular forms, the convolutions of the glands are











evidently determined by the location of other internal organs. Ondatra

and Neofiber best illustrate this condition. Clethrionomys has a more

generalized, recurved type, and Microtus, Pitymys and Pedomys are

intermediate.

The ampullary glands are rather constant in shape. In Baiomys,

these are reduced to several small tubular glands, unconnected, draining

into the respective vas deferens. Ochrotomys and Onychomys lack these

glands.

In several genera, particularly Nyctomys and Neotoma, the

ampullaries are large and filiform. This may be due to the absence of

the vesiculars, which generally form the anterior border for these

glandular masses.

In Tylomys a most distinctive condition exists. These are truly

"ampullary glands," draining into the ampulla directly. All others

enter the corresponding vas deferens, as well as the ampulla, by numer-

ous ducts. In larger forms (e.g., Ondatra) the ampullaries are con-

spicuously lobed. Whether this is a response to the large size of the

animal alone, is not known.

The prostate glands vary in form and number of pairs among the

various genera. The dorsal prostates occur in all but two genera

(Nyctomys and Neotoma). The ventral prostates are represented by either

one pair (seven genera), two pairs (16 genera), or are absent (Nyctomys

only). If two pairs of ventral prostates are present, one (lateral)

usually assumes a red color in FAA, the other (median) remains white.

Although this can probably be safely attributed to the nature of the

secretions of the respective glands, no further information is available.










The anterior prostates are present in 22 of 24 genera studied. They

are absent in Tylomys, and Onychomys. In two other genera, Neotoma

and Nyctomys. they are greatly enlarged and modified. This modification

of the anterior prostates occurs in the only two genera in which the

vesicular glands are also absent. In Ryctomys. these are the only

prostates that occur.

The homologies that I have attempted to ascertain in describing

these prostate glands are based on gross morphology and duct systems.

The problem exists, though, that if a basic "prostatic complement"

consists of (let us say), three pairs, evolution from this stock may

result in several forms having only two pairs: and it is not possible

at present to determine precisely which pairs have been lost in all

cases. The nature of the glandular secretions would be of much use to

the taxonomist as well as interest to the physiologist. How can the

sperm of presumably closely related animals such as Onychomys and

Peromyscus. exist in semen which is produced by two prostates and the

bulbo-urethrals in one form (Onychomys), and by four pairs of prostates,

vesiculars, ampullaries, and bulbo-urethrals in the other (Peromyscus)?

What is the fundamental importance of these glands? If one genus has

five sets of prostates and another only one, does the one of the latter

genus produce all that is produced by the five of the former? Perhaps

the female tract produces those substances not produced by the male. We

must admit that the physiological consequences of reduction, loss, or

addition of accessory glands is totally unknown.

In addition to secretary problems involving the prostates, the

fatty tissue with which the epididymides are invested is of interest.




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