THE URINO-GENITAL SYSTEM 283 



the posterior margin of the Hver, closely adherent to the abdominal 

 vein. Its walls, though thin, are well supplied with blood-vessels. 

 There is no direct connexion between the bladder and the ureters, 

 so that the urine can only gain access to it through the cloacal 

 chamber (see also p. 287). 



THE MALE SYSTEM (PI. XXI) 

 I. The Kidneys and Ureters. 



The chief differences to be observed between the kidney of the 

 male and that of the female are the sharper distinction between 

 the 'sexual kidney' and the 'definitive kidney', and the greater 

 relative size of the latter. The 'sexual kidney' in this sex is directly 

 associated with the gonad and serves to connect the vasa efferentia 

 with the Wolffian duct, while the sperms actually pass through its 

 tubules. Since Malpighian bodies are also present in the 'sexual 

 kidney' it is presumably able to secrete urine, and hence its duct 

 must be looked upon as a true urino-genital (Wolffian) duct. A 

 much more striking difference between the sexes is noticeable in the 

 ureters (utr.). In the first place although they are only small as they 

 leave the kidney, they expand very rapidly and become much larger 

 in the male and thicker walled (= appendices penis glandulosae, 

 Funk), and secondly the urino-genital duct draining the 'sexual 

 kidney' is not joined by the purely urinary ducts from the 'defini- 

 tive kidney' until quite close to their common entry into the cloaca. 

 Thus while the urino-genital (Wolffian) duct differs only in size 

 (and function) from the corresponding portion in the female, the 

 ureters proper consist of a series of about twelve C-shaped tubes of 

 gradually decreasing length pursuing a parallel course round the 

 ventro-lateral aspect of the kidney, until they finally enter a very 

 short common duct and pass through the cloacal wall. A com- 

 parison between Fig. 72 and Fig. 73 will make this clear. An 

 interesting comparative series (mainly of Japanese Urodeles) has 

 been worked out by Yamagiva (1924) which shows a progressive 

 dissociation of the true ureters from the urino-genital duct during 

 the course of evolution. 



The urino-genital duct appears at first sight to be continued for- 

 wards beyond the anterior end of the kidney, and in fact this was 

 believed by the older authors (Rathke, Bidder, &c.) to be the case. 

 Leydig (1853) demonstrated the tubular nature of this anterior 

 prolongation, and revealed it as the homologue of the Mullerian 

 duct of the female, although he does not actually call it such. 



