GLOMERULUS OF THE HEAD-KIDNEY. 109 



anteriorly, to sucli an extent that it soon appears as a shallow 

 oay in the body cavity. Thus each opening at this stage forms 

 a bay, wide and shallow anteriorly, becoming deeper and nar- 

 rower as we pass backwards, until finally behind it is separated 

 from the body cavity altogether, and there is seen in section a 

 Malpighian capsule precisely resembling a developing Malpig- 

 hian capsule in the hinder region of the Wolffian body.^ This 

 bay and in the small chamber behind, continuous with the bay 

 but separated from the body cavity, are together serially homo- 

 logous with a Malpighian capsule and the funnel leading from 

 it into the body cavity. In them a small glomerulus soon appears 

 attached to the dorsal wall. The glomerulus increases in size, 

 and the bay anteriorly widens out very much, while behind it 

 remains deep, and finally passes into the closed posterior por- 

 tion. The glomerulus fills up this passage which clearly runs 

 obliquely backwards and dorsalwards, and eventually, as far as I 

 can ascertain, the opening becomes completely closed, the epi- 

 thelium on the external glomerulus being no longer continued 

 through the opening on to the internal glomerulus. 



The external glomerulus, then, in the chick which has hither- 

 to been known as the glomerulus of the head-kidney, is nothing 

 more than a series of glomeruli of primary Malpighian bodies 

 projecting through the wide openings of the segmental tubes 

 into the body cavity. Their extreme antero-posterior extension 

 may be said to be within the ninth and thirteenth segments. 



In the chick the primary segmental tubes corresponding to 

 these external glomeruli are apparently never fully developed. 



I may mention that the external glomeruli are present in 

 greater numbers and attain a greater development in the duck 

 than in the chick. 



I defer the details and all discussion of this extraordinary and 

 unexpected development until I am able to publish a fuller paper 

 with figures. 



* Loc. cit., fig. 11. 



