154 DEVELOPMENT OF THE FROG. 



Wolffian body or kidney of the frog. The nephrostomes persist : 

 and in the adult frog as many as 200 or more are present on 

 the ventral surface of the kidney, as minute funnel-like ciliated 

 openings, leading by short tubes into the renal veins. 



4. The Wolffian and Miillerian ducts. 



So far we have only described one duct on each side, the 

 segmental duct, which acts as the excretory duct first of the 

 head kidney, and then of the Wolffian body as well. We have 

 now to consider in what way the ureters and generative ducts of 

 the adult frog are formed. 



About the time of the metamorphosis the head kidney, w^hich 

 has become rudimentary, separates completely from the duct, 

 which now ends blindly a short distance in front of the Wolffian 

 body. 



A little later, after completion of the metamorphosis and 

 entire disappearance of the tail, this anterior end of the 

 segmental duct, in front of the Wolffian body, becomes divided 

 somewhat obliquely into two; an anterior part, which is now 

 isolated from the Wolffian body, and will be called the 

 Miillerian duct; and a posterior part the Wolffian duct, which 

 is simply the posterior part of the original segmental duct, and 

 receives the Wolffian tubules of the kidney. 



The Miillerian duct becomes connected in 'front with the 

 peritoneal epithelium, and acquires an opening into the anterior 

 end of the body cavity. At its hinder end it grows back along 

 the outer side of the Wolffian duct to the cloaca, into which it 

 opens. So far the changes are the same in both sexes. In the 

 male frog the Miillerian duct persists in this condition through- 

 out life, and may be recognised as a slender longitudinal streak 

 lying in the thickness of the peritoneum a short distance to the 

 outer side of the kidney, and extending some distance in front 

 of it. In the female frog the Miillerian duct becomes the 

 oviduct, the anterior opening being carried forward first as a 

 groove, and then by closure of the lips as a tube, to the position 

 characteristic of the peritoneal opening of the adult oviduct; 

 while the posterior part becomes greatly convoluted and acquires 

 thick glandular walls: the hindmost part of the oviduct remains 

 thinner walled, but of much greater capacity. 



The Wolffian duct becomes in both sexes the ureter. In 

 the female frog it undergoes no further change of importance. 

 In the male frog the hinder end of the Wolffian duct becomes 



