UROGENITAL SYSTEM 



825 



stance which binds the spermatozoa into little packets called spermato- 

 phores. There are various accessory reproductive relations as mentioned 

 in the chapter on classification. 



Reptilia and Aves (Figs. 462, 465) : 



The kidneys are metanephric bodies which 

 pass their excretion through paired ureters 

 directly to the cloaca in the reptiles and 

 from here into a urinary bladder which, in turn, 

 empties into the cloaca. The pronephros never 

 functions, and the mesonephros (always lack- 

 ing nephrostomes) may function after hatch- 

 ing for a time in some reptiles. In the female 

 the mesonephros, after degenerating, is pre- 

 served as the "yellow-body." The male repro- 

 ductive organs consist of a pair of testes, a 

 pair of much coiled vasa deferentia through 

 which the sperm passes to the grooved penis; 

 the latter organ being attached to the front of 

 the cloaca. The female organs consist of 

 paired ovaries and large oviducts, provided 

 with albuminous and shell glands. The eggs 

 when laid are covered with a tough shell, and 

 those of reptiles are usually buried in the 

 ground. Many reptiles are, however, vivi- 

 parous. The Wolffian duct is the urinary tube 

 while the mesonephros functions, but later degenerates in the female. It 

 persists in the male as the vas deferens. 



In birds the left ovary alone remains functional. 



Mammalia : 



Only two pronephric tubules form and these never function. The 

 mesonephroi function in foetal life and in marsupials and monotremes 

 for sometime after birth. Nephrostomes never form except in Echidna. 

 In some rodents no glomeruli occur. The kidneys are of the metanephros 

 type. They are usually asymmetrical in position, one lying anterior to 

 the other. The ureters lead directly to the urinary bladder, which is 

 formed out of the remains of the allantois. 



The ovaries are never single as in birds. They are very small on 

 account of producing minute eggs with little or no yolk. This small 

 size of ovaries and eggs is well fitted to the habit of uterine gestation. 

 The paired oviducts enlarge to form paired uteri and in some groups 

 these unite into a single median uterus. 



The testes at firs.t lie in the body cavity as in reptiles, and occupy 

 positions homologous w r ith those of the ovaries. In most mammals with 

 the exception of monotremes, whales, elephants, armadillos, and a few 

 others, the testes descend into the scrotum. The penis of the male 

 mammal is homologous with the clitoris of the female. 



Fig. 465. 



Cloaca and urogenital 

 organs of a turtle, Chelydra 

 gerpentina. c, c' , blind sacs of 

 cloaca ; cl, cloaca ; e, epididymis 

 and vas deferens ; p, penis, r, 

 kidneys ; re, rectum ; , groove 

 on penis ; t, testis ; u, ureter ; 

 ug. t cloacal opening of bladder ; 

 v, bladder. (From Sedgwick's 

 Zoology, after Gegenbaur.) 



