270 MULLERIAN DUCT IN BIRDS. 



the Wolffian duct. I have satisfied myself, in conjunction with 

 Mr Sedgwick, that this is not the case, and that the general 

 account is in the main true ; but at the same time we have ob- 

 tained evidence which tends to shew that the cells which form 

 the Mullerian duct are in part derived from the walls of the 

 Wolffian duct. We propose giving a full account of our obser- 

 vations on this point, so that I refrain from mentioning further 

 details here. It may however be well to point out that, apart 

 from observations on the actual development of the Mullerian 

 duct in the Bird, the fact of its abdominal opening being 

 situated some way behind the front end of the Wolffian duct, 

 is of itself a sufficient proof that it cannot be the metamorphosed 

 front extremity of the Wolffian (= segmental) duct, in the same 

 way that the abdominal opening of the Mullerian duct is the 

 front extremity of the segmental duct in Elasmobranchs. 



Although the evidence I can produce in the case of the 

 Fowl of a direct participation of the Wolffian duct in the for- 

 mation of the Mullerian is not of an absolutely conclusive kind, 

 yet I am inclined to think that the complete independence of 

 the two ducts, if eventually established as a fact, would not of 

 itself be sufficient (as Semper is inclined to think) to dis- 

 prove the identity of the Mullerian duct in Birds and Elasmo- 

 branchs. 



We have, no doubt, almost no knowledge of the magnitude of 

 the changes which can take place in the mode of development of 

 the same organ in different types, yet this would have to be placed 

 at a very low figure indeed in order to exclude the possibility 

 of a change from the mode of development of the Miillerian 

 duct in Elasmobranchs to that in Birds. We have, it appears 

 to me, in the smallness of the portion of the segmental duct 

 which goes to form the Mullerian duct in Elasmobranchs, evi- 

 dence that a change has already appeared in this group in the 

 direction of a development of the Mullerian duct independent 

 of the segmental duct, and therefore of the Wolffian duct; 

 and it has been in view of this consideration, that I have de- 

 voted so much attention to the apparently unimportant point 

 of how much of the segmental duct was concerned in the for- 

 mation of the Mullerian duct. An analogous change, in a 

 somewhat different direction, would seem to be taking place in 



