COMPARATIVE ANATOMY. 



The testes remain constantly in the ab- 

 domen in the ornithorhynchus, the ele- 

 phant, the amphibious mammalia, and 

 the cetacea. Some animals have the 

 power of- protruding them from the ab- 

 domen, and retracing 1 them again into 

 the cavity ; as the bats, mole, hedge- 

 hog, and shrew, besides several of the 

 rodentia. They are thrust out of the ca- 

 vity, particularly at the rutting season. 



The tunica vaginalis exists constantly 

 in the mammalia. As the horizontal po- 

 sition of the body obviates the danger of 

 hernias, the cavity of this membrane 

 communicates by means of a narrow ca- 

 nal with the abdomen, in such animals as 

 have the testes remaining constantly in 

 the scrotum. 



In some species, where the act of copu- 

 lation requires a longer portion of time, 

 as in the dog, badger, &c. the corpus 

 spongiosum of the glans, and of the pos- 

 terior part of the penis, swells during 

 the act much more considerably than the 

 rest of the organ, and thus the male and 

 female are held together during a suffi- 

 cient space of time for the discharge of 

 the seminal fluid. 



Several species of mammalia, both 

 among those which possess no vesiculae 

 seminales, and thereby require a longer 

 time for completing the act of copulation, 

 and such as are not distinguished by 

 this peculiarity, possess a peculiar bone 

 in the penis, generally of a cylindrical 

 form, but sometimes grooved. This is 

 the case with some of the simise, most of 

 the bat-kind, the hamster, and several 

 others of the mouse-kind, the dog, bear, 

 badger, weasel, seal, walrus, &.c. 



In most of the mammalia the urethra 

 runs on the end of the glands, and forms 

 a common passage for the urine, pros- 

 tatic liquor, and semen. In some few 

 species, the passage which conducts the 

 two former fluids is distinct from that of 

 the seminal liquor. The bifid fork-like 

 glans, of the opossum has three openings, 

 one at the point of bifurcation for trans- 

 mitting the urine ; and two for the semi- 

 nal fluid at the two extremities of the 

 glans. The short urethra of the ornitho- 

 rynchus paradoxus opens directly into 

 the cloaca, and the large penis of the ani- 

 mal serves merely to conduct the semi- 

 nal fluid. It divides into two parts at its 

 extremity, and each of these is furnished 

 with sharp papillae, which are perforated 

 for the passage of the semen. A similar 

 structure obtains in the ornithorhynchus 

 hystrix, where the penis divides into four 

 g-lnuds. 



In some species of the cat-kind the 

 glans is covered with retroverted papillae, 

 which, as these animals have no vesiculae 

 seminales, may enable the male to hold 

 the female longer in his embraces. 



Lastly, it deserves to be mentioned, 

 that in some mammalia, the male penis, 

 while unerected, is turned backwards ; 

 so that the urine is voided in the male in 

 the same direction as in the female. The 

 hare, lion, and camel, afford instances of 

 this structure. But the statement which 

 has been so often repeated since the time 

 of Aristotle, that these retromingentia co- 

 pulate backwards, is erroneous. 



BIRDS. 



The testes, which lie near the kidneys, 

 and the ductus deferentes, are the only 

 male organs which are constantly found 

 in the whole class. 



In a very few instances, as in the cock, 

 the last mentioned canals terminate in a 

 dilated part, which has been considered 

 analogous to the vesiculae seminales. In 

 stead of a penis, most birds have in the 

 cloaca two small papillae, on which the 

 seminal ducts terminate. This is the case 

 in the cock, turkey and pigeon. 



Some few species have a simple penis 

 of considerable length, which is ordina- 

 rily concealed and retracted within the 

 cloaca ; but remains visible externally for 

 some time after copulation. It forms a 

 long worm-shaped tube in the drake, and 

 constitutes a groove in the ostrich, which 

 is visible when the animal discharges its 

 urine. 



AMPHIBIA. 



The kidney, testes, and epididymis, 

 lie close together in the testudines ; but 

 each of the three organs may be distin- 

 guished by its peculiar colour and struc- 

 ture on the first view. They appear to 

 have no vesiculae seminales : none at least 

 could be discovered in a testudo graeca, 

 which was lately dissected. The penis 

 on the contrary is very large ; and re- 

 tracted within the cloaca in its ordinary 

 state. Instead of an urethra, this part 

 contains a groove, whose margins ap- 

 proach to each other, when the part is 

 erected, so as to form a closed canal. 

 The glans terminates in an obtuse hook- 

 like point, somewhat resembling the end 

 of the elephant's trurtk. 



Serpents have long slender testicles ; 

 jio vesieuloe seminales ; but. a double pe- 



