WOLFFIAN BODIES. 411 



a later period, it opens into the allantois itself (Fig. 136, o, 

 vol. i. p. 381). 



The primitive kidney (primordial kidney) in the embryo 

 of Amriiota was formerly called the " Wolffian body," also 

 the " Okenian body." In all cases it acts for a time as a 

 true kidney, draining and secreting the useless fluids of the 

 embryonic body, and discharging them into the cloaca and 

 then into the allantois. The " primitive urine " collects in 

 the latter organ, and hence the allantois in the embryo of 

 man and of the other Amniota acts as a real urinary bladder, 

 or "primitive urinary sac;" yet it is in no way geneti- 

 cally connected with the primitive kidneys, but is rather, 

 as we have already seen, a pouch-like protuberance of the an- 

 terior wall of the terminal intestine (Fig. 135, u, vol. i. p. 380), 

 The allantois is, therefore, a product of the intestinal layer, 

 while the primitive kidneys are a product of the skin- 

 layer. Ph}dogenetically we must conceive that the allan- 

 tois originated as a pouch-shaped protuberance of the 

 cloacal wall resulting from the distension caused by the 

 collection in the cloaca of the primitive urine secreted 

 by the primordial kidneys. It is, originally, a blind sac 

 belonging to the rectum (Plate V. Fig. 15, hb). The true 

 urinary bladder of Vertebrates, evidently, first appeared in 

 Dipneusta (in the Lepidosiren), and was thence transmitted, 

 first to the Amphibia, and then to the Amniota. In the 

 embryo of the latter it protrudes far out of the yet unclosed 

 abdominal wall. Many Fishes, indeed, also possess a so- 

 called urinary bladder. But this is merely a local disten- 

 sion in the lower section of the primitive kidney ducts, 

 and hence, both in origin and in constitution, is essentially 

 distinct from the true urinary bladder. The two structures 



