EXISTENCE OF HEAD-KIDNEY IN THE EMBRYO CHICK. 7 



and situated some way behind the front end of the Wolffian duct. 

 In the next stage the three ridges connecting the grooves have 

 become more marked^ and in each of them a lumen has appeared, 

 opening at both extremities into the adjoining grooves. Still later 

 the ridges become more or less completely detached from the 

 peritoneal epithelium, and the whole head-kidney then consists 

 of a slightly convoluted duct, with, at the least, three peritoneal 

 openings, which is posteriorly continued into the Miillerian duct. 

 Still later the head-kidney atrophies, its two posterior openings 

 vanishing, and its anterior opening remaining as the permanent 

 opening of the Miillerian duct. The glomerulus arises as a 

 vascular prominence at the root of the mesentery, slightly prior 

 in point of time to the head-kidney, and slightly more forward 

 than it in position. We have not traced its atrophy, 



We stated in our preliminary paper that the peculiar struc- 

 tures we had interpreted as the head-kidney had completely 

 escaped the attention of previous observers, though we called 

 attention to a well-known figure of Waldeyer^s (copied in the 

 'Elements of Embryology,' fig. 51). In this figure a connec- 

 tion between the germinal epithelium and the Miillerian duct is 

 drawn, which is probably part of the head-kidney, and may be 

 compared with our figures (Series b, No. 8, and Series d. No. 4). 

 Since we made the above statement. Dr. Gasser has called our 

 attention to a passage in his valuable memoir on ' The Develop- 

 ment of the Allantois,'^ in which certain structures are described 

 which are, perhaps, identical with our head-kidney. The fol- 

 lowing is a translation of the passage : — 



" In the upper region of Miiller's duct I have often observed 

 small canals, especially in the later stages of development, which 

 appear as a kind of doubling of the duct, and run for a short 

 distance close to Miiller's duct and in the same direction, open- 

 ing, however, into the body cavity posterior to the main duct. 

 Further, one may often observe diverticula from the extreme 

 anterior end of the oviduct of the bird, which form blind pouches 

 and give one the impression of being receptacula seminis. Both 

 these appearances can quite well be accounted for on the supposi- 

 tion that an abnormal communication is etfected between the 

 germinal epithelium and Miiller's duct at unusual places ; or 

 else that an attempt at such a communication is made, resulting, 

 however, only in the formation of a diverticulum of the wall of 

 the oviduct." 



The statement that these accessory canals are late in developing, 

 prevents us from feeling quite confident that they really cor- 

 respond with our head-kidney. 



1 'Beitrage zur Entwick lungsgescbiohte d. AUantois der Miiller'scliea 

 Gange u. des Afters.' Frankfurt, 1874. 



