1880.] Mr Sedgivick,' Glomerulus of the head-kidney.' 379 



(2) Adam Sedgwick, B.A., On the development of the structure 

 knoiun as the 'glomerulus of the head-kidney' in the chick. 



In a paper by Mr Balfour and myself in the Quart. Journ. of 

 Micr. Science, Vol. Xix., 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 identified it as an 

 homologous structure. 



Gasser^ has also independently discovered and similarly identi- 

 fied 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 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 con- 

 necting the glomerulus with the attachment of the mesentery 

 varies in thickness in difi'erent 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 glo- 

 merulus breaks away. At the stage we are describing no true Mal- 

 pighian bodies are present in the part of the Wolffian body on the 

 same level with the anterior end of the glomerulus, but the Wolf- 

 fian body merely consists of the Wolffian duct. At the level 

 of the posterior part of the glomerulus this is no longer the case, 

 but here a regular series of primary Malpighian bodies is present, 

 and the glomerulus of the head-kidney may frequently be seen 

 in the same section as a Malpighian body. In most sections the 

 two bodies appear quite disconnected, but in those sections in 

 which the glomerulus of the Malpighian body comes into view 

 it is seen to be derived from the same formation as the glomerulus 

 of the head-kidney." 



The point which is left in doubt in the above description, 

 viz. as to whether the glomerulus constitutes a continuous struc- 

 ture, is at once decided by a study of its development. 



1 Sitzuvgsherichte der Gesellschaft zur Beford d. gesam. Natuj-wins., No. 5, 1879. 



