canal of the mesonephric kidney. From the marginal canal 

 the coiled tubuli mesonephroi lead to the ductus epididy- 

 midis, the anterior end of the nephric duct. The many vari- 

 ations in the testis-kidney connections suggest great plas- 

 ticity of development in this area. 



The epididymis is well developed and may extend far pos- 

 teriorly before giving way to the slightly convoluted vas de- 

 ferens. The deferent duct joins the ureter of its side, and 

 they open together at the tip of a urogenital papilla. The 

 ducts of either side open through separate papillae. In some 

 reptiles the ureter and vas deferens open separately into the 

 urogenital sinus. The urogenital sinus may be only a pocket 

 of the cloaca lying behind the openings of the anus and the 

 ventral bladder. A vestigial Mullerian duct lies along the 

 body wall lateral to the testis and reproductive tract in 

 general. 



Two different kinds of intromittent organs are found in 

 reptiles, but Sphenodon lacks such a structure. The lizards 

 and snakes agree in having hemipenes. These are bilateral 

 sacculations of the cloaca (Figure 10-8 B). These sacs ex- 

 tend posteriorly below the skin. When everted, one at 

 a time, they protrude through the cloacal aperture. The 

 distal end is large and rounded, and the stem tapers to a 

 narrow base which attaches at the anterolateral cloacal wall. 

 The structure is grooved to conduct the sperm from the 

 cloacal cavity of the male to that of the female, into which 

 it is everted. The surface of the everted hemipenes is studded 

 with spines. 



In turtles and crocodilians there is a grooved penis in the 

 floor of the cloaca (Figure 10-38). This contains fibrous and 

 perhaps erectile tissue, a corpus fibrosum. The penis of the 

 turtle is suggestive of that of the primitive mammal, except 

 that it is not sheathed in a pouch. That of the crocodile is 

 simpler and like that of the bird. 



The testes of the bird are comparable to those of the lizard 

 (Figure 10-10). The testis lies below the anterior part of the 

 kidney rather than anterior to the kidney. Connection v«th 

 the kidney tubules involves an irregular cavity, the antrum, 

 into which the tubuli recti of the seminiferous tubules open 

 on the one side and from which on the other side a number 

 of efferent ducts (10 to 12) pass into the epididymis. The an- 

 trum represents the rete testis. 



The deferent duct opens posteriorly into the proctodeum, 

 just as in the crocodilian. In the males of most of the perch- 

 ing birds, the terminal part of the duct becomes quite 

 elongated and coiled at the breeding time. A "glomus," or 

 tubular mass, is thus formed, which, along with the terminal 

 ampulla of the duct, causes the cloacal aperture to bulge 

 outward. 



In the bird, but also in reptiles and many mammals, the 

 testes undergo a drastic change in size during the course of 

 the year. In the nonbreeding period they are much smaller 

 than at the breeding time. 



The female The ovary of the reptile differs only in that 

 very large, yolked eggs are produced (Figure 10-9). As a re- 



TURTLE 



bulb of corpus cavernosum 



cloacal pouch or accessory bladder 



corpus fibrosum 

 retractor penis muscle 



bladder 



^ urogenital sinus 



cloacal pouch 



.corpus 



cavernosum 



CROCODILE 

 coprodeum urodeum 



^^e^^'' vas deferens 



proctodeum 



cloacal gland 

 corpus fibrosum 



urodeum 



vas deferens 



^coelomic canal 

 bulb of corpus cavernosum 



corpus fibrosum 

 retractor penis muscle 



proctodeum 

 urodeum 



coelomic canal 

 corpus fibrosui 



B 



H 



Figure 10-38. The penis of the turtle and crocodile. A, sagittal section through cloaca of turtle; 

 B, C, D, three cross sections (indicated in A) showing interrelations of parts; E, sagittal section of 

 cloaca of crocodile; F, G, H, three cross sections (indicated in E) showing interrelations of parts. 

 (After Ihle et al, 1927) 



324 . THE UROGENITAL SYSTEM 



