UROGENITAL ORGANS 



369 



Several reptiles have cloacal glands (a single dorsal pair in snakes, a lateral 

 pair added in lizards) of uncertain function. The crocodiles have a pair of 

 'musk-glands' in the same region, the distal end of their ducts being pro- 

 trusible. The adrenal glands of the sauropsida are intimately associated with 

 each other, the trabeculae of suprarenals and interrenals being commingled 

 except in lizards and turtles where the suprarenal tissue is on the dorsal side of 

 the interrenal. 



MAMMALS. — In the mammals but two pronephric tubules are 

 outlined in development and these are never functional excretory 

 organs. The pronephric duct is first a solid cord on the surface of the 

 nephrotomic segments and later it becomes canalized. Of the fate 



Fig. 392. — Urogenital organs in pig 

 embryo 67 mm. long, after Klaatsch. a, 

 allantois. g, gonad; ms, mi, meso- and 

 metanephroi; sr, adrenal. 



Fig. 393. — Lobulated kidney 

 (metanephros) of otter, Lutra cana- 

 densis (Princeton, 2234). c, aorta; 

 u, ureter; v, postcava. 



of the pronephros little is known. The mesonephros, on the other 

 hand, is an important structure in foetal life (fig. 392), and in mar- 

 supials and monotremes it continues to function for some time after 

 birth. Later it disappears in all, with the exception of the parts 

 concerned in the formation of the efferent ductules of the testes, and 

 some other inconsiderable remnants in both sexes (fig. 368, C, D). 

 Nephrostomes are formed only in Echidna, and in some rodents no 

 glomeruli occur. 



The permanent kidney (metanephros) is, in the young stages, 

 lobulated, a result of the peculiar development (p. 344), the lobules 



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