354 



COMPARATIVE ANATOMY 



CvAo 



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 (Fig. 279), 

 while the former becomes connected in the male with the 

 generative organs. Delicate vasa efferentia, developed from the 

 mesonephros, pass out from the testis (Figs. 279, 280, 

 292) into the substance of the kidney, and there open into the 

 renal tubules; they may either enter the kidney direct, or 



else open first into a longitudinal 

 collecting duct, from which fine 

 canals pass to the tubules. Thus 

 the seminal fluid passes through 

 the nephridia as well as through 

 the Wolfnan 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 (compare Elasmobranchs, 

 p. 350). In Anura the Wolffian 

 ducts pass some distance indepen- 

 dently along the body-cavity, in 

 correspondence with the position 

 of the kidneys, and a seminal 

 vesicle opens into each (Fig. 281). 

 The urinary (allantoic) bladder 

 (see p. 259) opens into the cloaca 

 ventrally, opposite to the urino- 

 genital apertures. In its simplest 

 form it is finger-shaped (e.g., Siren, 

 Proteus), but it usually becomes 

 swollen distally and is often bi- 

 lobed : in Alytes and Bombinator 

 it forms a double sac. 



Slight indications of a seg- 

 mental arrangement are found only 

 in the anterior sexual portion of 



the kidney of Urodeles ; in the posterior part, and in the entire 

 kidney of Anura, all traces of segmentation have disappeared. In 

 both cases, however, the nephrostomes remain throughout life 

 in great numbers on the ventral surface of the kidney, which 

 is covered over by the peritoneum (Fig. 281). 



The nephrostomes are connected with the urinary tubules in larval Anura, 

 but later on they become separated from them, and open into the renal 



FIG. 280. MALE URINOGENITAL 

 ORGANS OF Rana esculenta. 



Ur, Ur, Urinogenital (Wolffian) 

 ducts, which appear on the lateral 

 surface of the kidneys at f; 8, 

 S', their apertures into the cloaca 

 (Cl) ; Ho, Ho, testes ; FK, FK, 

 corpora adiposa ; Cv, postcaval 

 vein ; Ao, aorta ; Vr, revehent 

 renal veins. 



