18 ADAM SEDGWICK. 



that the continuous ridge extends from the 7th to the 11th 

 segments. 



With regard to Gasser^s statement of the complete isolation 

 of the duct in the anterior region from the intermediate cell 

 mass, I can only say that my observations point to an entirely 

 different conclusion. 



Thirdly, I differ with him in his statement that the duct in 

 the growth back from the attached extremity does not come 

 into relation with adjacent structures. 



As stated above, it seems to me that for the space of four 

 segments the small cord of cells which grows back from the hind 

 end of the ridge, does almost immediately become connected 

 with the intermediate ceil mass. 



Development of the Wolffian Duct and Body from the V2t/i — Ibth 



Segment. 



I now pass to the most interesting point which has turned 

 up in my investigations on the excretory system of the chick. 



In a paper by Mr. Balfour and myself,^ describing the develop- 

 ment of what we believed to be a rudimentary head-kidney in 

 the chick, we drew attention to a structure which so closely re- 

 sembled the glomerulus^ of the head-kidney of the Ichthyopsida 

 that we identified it as an homologous structure. 



Gasser^ has also independently discovered and similarly iden- 

 tified this structure. 



In the paper just referred to no attempt was made to trace the 

 development of this glomerulus, but it was merely described as 

 it appeared at the time of its greatest development. 



The following description is taken from that paper : 



"In the chick the glomerulus is paired, and consists of a 

 vascular outgrowth or ridge projecting into the body cavity on 

 each side at the root of the mesentery. It extends from the 

 anterior end of the Wolffian body to the point where the fore- 

 most opening of the head-kidney commences. We have found 

 it at a period slightly earlier than that of the first development 

 of the head-kidney. ...In the interior of this body is seen a 

 stroma with numerous vascular channels and blood-corpuscles, 

 and a vascular connection is apparently becoming established, if 

 it is not so already, between the glomerulus and the aorta. The 

 stalk connecting the glomerulus with the attachment of the 



1 'On the Existence of a Head-Kidney in the Embryo Cliick: Studies 

 from the Morplioloiiical Laboratory in the University of Cambridge,' Part 1, 

 1880, and 'Quart. Journ. of Micr. Science,' vol. xix. 



2 1 have already j^'iveu a preliminary account of the development of this 

 structure in the ' Proc. Cambridge Pliil. Soc.,' May 3, 1880. 



3 ' Sitzungsberichte der Gesellschait zur Bedford d. gesam. Naturwiss.,* 

 No. 5, 1879. 



