On the Development of the Steucture known as the 

 ' Glomerulus of the Head-Kidney' in the Chick. 

 By Adam Sedgwick, B.A. 



In a paper by Mr. Balfour and myself {vide p. 1 — 20 

 of "these Studies"), describing the development of what we 

 believed to be a rudimentary head-kidney in the chick, we 

 drew attention to a structure which so closely resembled the 

 glomerulus of the head-kidney of the Icthyopsida that we iden- 

 tified 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 its time of greatest development. 



The following description is taken from that paper : 



" In the chick the glomerulus is paired and consists of a vas- 

 cular 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 foremost open- 

 ing 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 vas- 

 cular 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 mesentery 

 varies in thickness in different sections, but we believe that the 

 glomerulus is continued unbroken throughout the very consider- 

 able region through which it extends. This point is, however, 

 difficult to make sure of, owing to the facility with which the 

 glomerulus breaks away. At the stage we are describing no 

 true Malpighian bodies are present in the part of the Wolffian 

 body on the same level with the anterior end of the glomerulus, 

 but the Wolffian body merely consists of the Wolffian duct. At 

 the level of the posterior part of the glomerulus this is no logger 



' ' Sitzungsberichte der Gesellscbaft zur Belord d. eesain. Natui wiss.,' 

 No. 5, 1879. 



