366 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



rately into the cloaca (fig. 387). Only in lizards and turtles is there a well- 

 developed urinary bladder of the allantoic type (fig. 358) although an allantois 

 is present in the development of all, and urinary bladders, sometimes dorsal, 



sometimes ventral to the cloaca, are common 

 in the embryonic stages. The urine in other 

 sauropsids is semisolid and consists largely of 

 uric acid. 



The gonads are roughly correlated in shape 

 with that of the body and often there is a lack 

 of symmetry between the two sides of the animal. 

 Thus in reptiles and birds there is a marked 

 tendency for the gonad of one side to be farther 

 forward than is the other, and in birds this goes 

 so far that in the female the ovary of the right 

 side may be degenerate or even may be entirely 

 lost. 



The Wolffian duct is the vas deferens in 



the male and the anterior end of the meso- 



nephros forms the connexion of the testis with 



the duct, the two constituting an epididymis, 



which usually is small in birds, but larger than 



the testis in many reptiles. In most reptiles 



I J ■ ) i/-~>« the ureter and vas deferens of a side have a 



1 I '^^ iuj^}h~-m common opening to the cloaca, but in birds they 



1 I i // / ^'■^ distinct (fig. 388, B). Miiller's duct often 



1 I ; I 1^^ persists in the male, sometimes with a lumen and 



an ostium, and in Lacerta viridis, the common 



green lizard of Europe, it is as well developed 



as in the female. 



The ovaries are saccular with an internal 

 lymphoid cavity, and the walls are rich in 

 blood-vessels, in correlation with the relatively 

 enormous eggs. In some lizards the right 

 ovary is farther forward and larger than the 

 left, a contrast to the conditions in birds men- 

 tioned above. Corresponding to the reduction 

 of the right ovary of birds, the oviduct of that 

 side is reduced or may be practically absent. 

 In all sauropsida each oviduct opens to the 

 ccelom by a large, slit-like ostium (fig. 388) and 

 the tube, usually longitudinally plaited, is dif- 

 ferentiated into regions with different functions. 

 In Sphenodon, crocodiles, turtles and birds the 

 first part of the oviduct secretes the albumen (white) of the egg, which is lack- 

 ing from the eggs of snakes and lizards. Farther down is an enlargement, called 

 the uterus or shell gland, which secretes the shell with its organic base and, in 

 birds and some reptiles, its large amount of lime. The eggs are forced along 

 the oviducts by the action of the muscles in their walls. 



Fig .387. — Urogenital organs 

 of Monitor, after Gegenbaur. 

 d, opening of digestive tract into 

 cloaca; e, epididymis; k, kidney; 

 p, papillae of urogenital system; 

 r, rectum; t, testes; «, ureter; vd, 

 vas deferens. 



