UROGENITAL SYSTEM. 



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long in the caecilians (fig. 334) and Amphiuma, saccular in most urodeles, and bifid 

 at the tip in most anura, being even divided into two sacs, connected only at the 

 opening into the cloaca in some species. 



SAUROPSIDA. In reptiles and birds, as in all amniotes, the pronephros is 



rudimentary at all stages and never functions as 

 an excretory organ. The mesonephros takes its 

 place in fcetal life, and in some it continues to 

 function for some time after hatching, but in all it 

 is eventually replaced by the metanephros, though 

 its degenerate remains persist in the reptiles (better 

 preserved in the female) forming the so-called 

 'golden yellow body.' Another part is retained 

 in the male as a part of the efferent ductules of 

 the testes, somewhat as in mammals. 



The metanephros (fig. 328) never has the ex- 

 tent of the mesonephros of the ichthyopsida, but 

 it is usually restricted to the posterior half of the 

 body cavity, often to the pelvic region. It is usu- 

 ally small and compact (snakes form an exception) 

 or somewhat lobulated, in the snakes the tabulation 

 sometimes being so extensive that the lobules are 

 only connected by the ureter. In the lizards the 



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ll.il 



FIG. 328. FIG. 329. 



FIG. 328. 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; u, ureter; vd, vas deferens. 



FIG. 329.- Urogenital organs in pig embryo 67 mm. long, after Klaatsch. a, allantois; 

 g, gonad; ms, mt, meso- and metanephroi ; sr t adrenal. 



organs of the two sides may be connected behind. In the birds there are usually 

 three lobes in each mesonephros, these lying in cavities in the pelvis between 

 the sacral vertebrae and the transverse processes. 



