312 



MARSUPIALIA. 



but in this circumstance we may perceive an 

 example of the retention of a typical structure 

 at the deeper seated part of a system of organs, 

 when not incompatible with a slight modifi- 

 cation of a peripheral segment of the same 

 system ; it being by no means obviously neces- 

 sary to abrogate the division of the urethral 

 bulb simply because the blood accumulated 

 in each division was to be driven in a concen- 

 trated current upon a single, instead of a dou- 

 ble glans penis. 



The intermediate structures of the glans be- 

 tween the two extremes above instanced are 

 presented by the Ursine Dasyure, Koala, and 

 Wombat. In the Koala (jig. 135, B) the glans 

 penis terminates in two semicircular lobes, and 

 the urethra is continued by a bifurcated groove 

 along the mesial surface of each lobe. In the 

 Wombat f^'g. 135, C)thereisasimilarexpansion 

 of the urethra into two divergent terminal grooves, 

 but the glans is larger, cylindrical, and par- 

 tially divided into four lobes :* the chief struc- 

 ture of interest in this part of the Wombat is 

 the callous external membrane of the glans, 

 and its armature of small recurved, scattered 

 horny spines, which do not occur in any other 

 Marsupial animal. The small retroverted pa- 

 pillae on the infundibuliform glans of the 

 Koala and on the bifurcate glans of the Phalan- 

 gers and Petaurists are not horny. 



In the Perameles lagotis not only is the glans 

 bifurcate, but each division is perforated, and 

 the urethral canal is divided by a vertical 

 septum for about half an inch before it reaches 

 the forked glans. From the septum to the bladder 

 the canal is simple, as in other Marsupials. 

 The bifurcations of the glans in the Opossums 

 and Phalangers are simply grooved. 



If the experiments of Haighton and the 

 detection, by Drs. Bischoffand Barry, of sper- 

 matozoa upon the ovary itself after coitus, 

 had not rendered the question of the neces- 

 sity of the contact of the semen with the 

 ovarium for impregnation almost independent 

 of the aid of Comparative Anatomy, the diffe- 

 rences of structure above described in the 

 urethra and glans penis of the Marsupial 

 animals would have gone far to explode the 

 once prevalent notion of an ' aura seminalis* 

 fertilizing the ovum through the medium of 

 the circulating fluid : for why, on such an 

 hypothesis, should the impregnation of two 

 ovaria, each communicating with a distinct 

 oviduct, uterus, and vagina, as in the Opos- 

 sum, require two conduits of the semen in the 

 male, one for each vagina? and wherefore, 

 in the case of an uniparous Marsupial, in 

 which the fecundating stream need ascend only 

 to a single ovarium, as in the Kangaroos and 

 Potoroos, is the penis terminated by a single 

 glans ? 



The spermatozoa of the Perameles have a 

 single barb at the base of the head, which is 

 sub-elongate and compressed ; in other respects, 

 as in size and proportion of the filamentary tail, 

 they resemble the spermatozoa of the Rabbit. 



* Cuv. Lemons d'Anat. Comparce, 1805, t. v. 

 p. 91. 



Neither in the Kangaroo, Phalanger, nor Da- 

 syure did the spermatozoa present a spiral head 

 or any noticeable deviation from the characters 

 of the spermatozoa in the smaller placental 

 quadrupeds : those of the Dasyure have a 

 node at the base of the head. 



The corpus cavernosum penis commences by 

 twocrura(c/, d, figs. 135, 136), neither of which 

 have any immediate attachment to the bony pelvis. 

 Cuvier correctly states, that in the Kangaroo the 

 two cruraof the corpus cavernosum, and the two 

 bulbs of the corpus spongiosum, soon unite to 

 form a single cylindrical body, having a canal 

 which nearly follows the direction of its axis, 

 whose parietes are equally strong and fibrous, 

 and which contains the urethra; so that the 

 transverse section of the corpus cavernosum 

 resembles a ring ; but the two lateral cavities 

 are separated by two vertical septa which ex- 

 tend one from the central canal to the dorsuin 

 penis, the other from the central canal to the 

 inferior wall of the penis.* 



In the Kangaroo and Potoroo, the erectores 

 penis (Jig. 135 d, d) arise by a thin fascia from 

 near the lower part of the symphysis pubis, soon 

 become fleshy, and increase in thickness as they 

 pass outwards : each muscle then returns upon 

 itself, at an acute bend, to grasp the crus penis, 

 and terminates in a strong tendinous expansion 

 at the junction of the cavernous with the bul- 

 bous structure. 



Fig. 136. 



Male Organs, Opossum. 

 (Cuu'per, I. c.) 



The retractor penis (fgs \ 35, 1 36, g, g) arises 

 in the Kangaroo from the middle of the sa- 

 crum, and divides into two muscles, behind the 

 rectum, opposite the dilated commencement 

 of the musculo-prostatic part of the urethra; 

 each division diverges to the side of the rectum, 

 then passes to the interspace between the rec- 

 tum and roots of the penis, and along the 



* Le9ons d'Anat. Comp. 180.3, t. v. p. 73. 



