530 



OF SECRETION. 



Fig. 155. 



Fig. 156. 



Uriniferous Tube, Malpighian Tuft and Capsule, 

 from Kidney of Frog; a, cavity of the tube; b, 

 epithelium of the tube; 6', ciliated epithelium of 

 the neck of the capsule; b", detached epithelium 

 scale ; c, basement membrane of tube ; e' , basement 

 membrane of capsule. Magnified about 320 dia- 

 meters. (After Bowman.) 



Distribution of the Renal vessels, from Kidney 

 of Horse ; a, branch of renal artery ; a/", afferent 

 vessel ; m, m, Malpighian tufts; tf, rf, efferent ves- 

 sels; p, vascular plexus surrounding the tubes; 

 st, straight tube; ct, convoluted tube. Magnified 

 about 30 diameters. (After Bowman.) 



ney.* The development of 

 day. They are seen on the 



157. 



Corpora Wolffiana, with kidney 

 and testes, from embryo of Bird ; 

 1, kidney; 2, 2, ureters; 3, corpus 

 Wolffianum ; 4, its excretory duct ; 

 5, 5, testicles; at the summit are 

 seen the supra-renal capsules. 

 (After Miiller.) 



the true Kidneys commences in the Chick about the fifth 

 sixth, as lobulated grayish masses, which sprout from the 

 outer edges of the Wolffian bodies ; and they gradually 

 increase, the temporary organs diminishing in the same 

 proportion. The sexual organs, as will be hereafter ex- 

 plained ( 699), also originate in the Wolffian bodies ; and 

 at the end of foetal life, the only vestige of the latter is to 

 be found as a shrunk rudiment situated near the testes of 

 the male. The progress of development in the Human 

 embryo seems closely conformable to the foregoing ac- 

 count. The Wolffian bodies begin to appear towards the 

 end of the first month; and it is in the course of the sev- 

 enth week, that the true Kidneys first present themselves. 

 From the beginning of the third month, the diminution in 

 the size of the Wolffian bodies goes on part passu with the 

 increase of the Kidneys: and at the time of birth, scarcely 

 any traces of them can be found. At the end of the third 

 month, the kidneys consist of seven or eight lobes, the fu- 

 ture pyramids; their excretory ducts" still terminate in the 

 same canal which receives those of the Wolffian bodies 

 and of the sexual organs ; and this opens, with the rectum, 

 into a sort of cloaca, or sinus urogenitalis, analogous to 

 that which is permanent in the oviparous Vertebrata. The 

 Kidneys are at this time covered by the Supra-Renal Cap- 

 sules, which are very large ; about the sixth month, how- 

 ever, these have decreased, whilst the kidneys have in- 

 creased, so that their proportional weight is as 1 to 2. At 

 birth, the weight of the Kidneys is about three times that 

 of the Supra-Renal Capsules; and they bear to the whole 

 body the proportion of 1 to 80: in the adult, however, they 



See Principles of General and Comparative Physiology, 659. 



