150 Mr MacBride, On the Development [Feb. 9, 



tinued out over the surface of the pronephros arid beyond it, as 

 Hoffmann has described. The groove, traced backwards for 15 

 sections, becomes a canal, which after two sections ends in a solid 

 thickening of the peritoneum. In succeeding stages the groove 

 extends ventrally, as described by Hoffmann, and in the last stage 

 it has become a canal, opening somewhat ventrally, the opening 

 having already acquired the fimbriae of the adult orifice. But 

 I have been quite unable, after examining a number of adults, to 

 detect any important difference between the position of the ab- 

 dominal opening in my last stage and that of the adult funnel. 

 The latter is not situated dorsally but at the side of the lung. It 

 is fimbriated, and these fimbriae are continued, lying in a groove, 

 on to the mesentery connecting the stomach and liver, over the 

 ventral surface of the lung. It is true that the length of the 

 orifice appears to have extended- somewhat in a dorsal direction, 

 but that is all. 



As to the origin and backward growth of the duct behind the 

 funnel, I find that the mode of origin described by Hoffmann for 

 its hinder portion holds for its entire length. It has been men- 

 tioned above that in the earliest stage the peritoneal groove, 

 traced backwards, ends in a slight thickening of the peritoneum. 

 The next stage shows the same condition of things; but a good 

 length of the groove has been converted into a canal. In the first 

 stage the Wolffian duct is still discernible in the part of the body 

 in front of the mesonophros, but it is reduced to a rod of pale 

 degenerate cells. There is no indication of any splitting such as 

 Hoffmann described ; and it appears a priori in the highest 

 degree improbable that fresh development should take place from 

 such an atrophied rudiment. I may mention that Hoffmann 

 omits to give any figures illustrating this point. In frogs of this 

 age (that is to say those in which the tail is about as long as the 

 body), there is a distinct line of epithelium on the outer border of 

 the kidney, reaching back to the cloaca, which is distinguished 

 from the rest of the peritoneum by its more columnar character. 

 In succeeding stages, all trace of the Wolffian duct in front of the 

 kidney is gone ; and the thickening of the peritoneum mentioned 

 above travels back along this line of modified epithelium. I have 

 called it a peritoneal thickening because I believe it to be derived 

 from the peritoneum. It appears in sections as a projecting 

 nodule of deeply staining tissue, the outermost cells of which pass 

 at the side into the ordinary peritoneum. Furthermore, although 

 the rudiment in front of the kidney grows back with some regu- 

 larity, behind the kidney it is formed long before one can trace it 

 at the side of this organ. It nowhere comes in contact with the 

 Wolffian duct. But it is not possible to speak with absolute cer- 

 tainty as to the origin of the cells which compose this solid rudi- 



