URINARY ORGANS 



457 



Cv Ao 



FK 



354). This condition sometimes persists in the anterior portion of 

 the kidney, but owing to secondary processes of growth, as 

 many as twenty nephrostomes are later on met with in a single 

 body-segment. The number of nephrostomes in the entire kidney 

 may amount to a thousand or more. As regards the urinary duct 

 and the relations of the entire renal apparatus to the generative 

 organs, the Gymnophiona in all essen- 

 tial points resemble other Amphibia. 

 The kidneys of Urodela and 

 Anura are situated in the usual 

 position on the dorsal side of the 

 body-cavity ; in the former they 

 are band-like and more extended 

 longitudinally than in the latter, 

 in which they are shorter and more 

 compact, and are confined to the 

 middle portion of the ccelome. 



In Urodeles they always consist 

 of a narrow anterior, and a broader 

 and more compact posterior portion. 

 The latter, as in Elasmobranchs, 

 gives rise to the functional kidney, 

 while the former becomes connected 

 in the male with the generative 

 organs. Delicate vasa efferentia, 

 developed from the mesonephros, in 

 all cases pass out from the testis 

 (Figs. 342, 355) into the substance 

 of the kidney, and there open into 

 the mesonephric tubules ; they may 

 either enter the kidney direct, or 

 else open first into a longitudinal a0 rta- 



collecting duct, from which fine 

 canals pass to the tubules. Thus 

 the seminal fluid passes through the 

 nephridia as well as through the 

 Wolffian duct, which serves as a 

 urinogenital duct. 



In Urodela and Anura of both sexes the Wolffian duct nearly 

 always opens separately on either side into the cloaca, receiving 

 first, in Urodeles, a number of ducts from the posterior part of the 

 kidney (cf. Elasmobranchs). In Anura the Wolffian ducts 

 pass some distance independently along the body-cavity in corre- 

 spondence with the position of the kidneys, and a seminal vesicle 

 (not present, e.g., in Rana esculenta) may open into each (Fig. 344). 

 The urinary bladder, representing the entire allantois (cf. p. 437) 

 opens into the cloaca ventrally, opposite to the urinogenital 

 apertures. In its simplest form it is finger-shaped (e.g. Siren, 



FIG. 343. MALE URINOGENITAL 

 ORGANS OF Rana esculenta. From 

 the ventral side. 



Cv, postcaval vein ; 

 FK, corpus adiposum ; Ho, testis ; 

 S, S', apertures into the cloaca 

 (Cl) of Ur, urinogenital (Wolffian) 

 ducts, which appear on the lateral 

 surface of the kidneys at t ; Vr, 

 revehent renal veins. 



