626 EXISTENCE OF A HEAD-KIDNEY 



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 suppo- 

 sition that an abnormal communication is effected 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 de- 

 veloping, prevents us from feeling quite confident that they 

 really correspond with our head-kidney. 



Before passing on to the other parts of this paper it is neces- 

 sary to say a few words in justification of the comparison we 

 have made between the modified abdominal extremity of the 

 Miillerian duct in the chick and the head-kidney of the Ichthy- 

 opsida. 



For the fullest statement of what is known with reference to 

 the anatomy and development of the head-kidney in the lower 

 types we may refer to Spengel and Fiirbringer 1 . We propose our- 

 selves merely giving a sufficient account of the head-kidney in 

 Amphibia (which appears to be the type in which the head- 

 kidney can be most advantageously compared with that in the 

 bird) to bring out the grounds for our determination of the 

 homologies. 



The development of the head-kidney in Amphibia has been 

 fully elucidated by the researches of W. Mliller 2 , Gotte 3 , and 

 Fiirbringer 4 , while to the latter we are indebted for a knowledge 

 of the development of the Miillerian duct in Amphibians. The 

 first part of the urino-genital system to develop is the segmental 

 duct ( Vornieregang of Fiirbringer), which is formed by a groove- 

 like invagination of the peritoneal epithelium. It becomes con- 

 stricted into a duct first of all in the middle, but soon in the 



1 Loc. cit. 



'-' Jt'iiaische Zeitschrijt, Vol. IX. 1875. 



3 Rntwickelungsgeschichte d. Unke. 



4 Loc. cit. 



