ON THE SUPRARENAL BODIES OF VERTEBRATA. 
145 
body, of a blastema such as I have described seems to throw 
doubt on the correctness of such a view ; though I have un- 
fortunately been unable, owing to want of material, to prove 
by examination of later stages the share which this blastema 
takes in the formation of the paired anterior suprarenals. 
In the chick, as might perhaps have been expected, from the 
highly-modified development of the whole kidney, the mode 
of origin of the suprarenal blastema differs in many important 
points from that which has been described for the dogfish and 
for the lizard. 
Before the fourth day of incubation there is no trace of any 
suprarenal rudiment whatever. By about the end of this day, 
however, certain large cells, the rudiments of the cortical sub- 
stance, make their appearance in the indifferent mesoblast at 
the inner side of the mesonephros. The exact mode of origin 
of these cells I have been unable to determine. At their first 
appearance they lie, singly or in groups of two t)r three, in the 
mesoblast between the aorta and the kidney, being distin- 
guished from the surrounding cells by their rounded, un- 
branched form, their larger size, and the clearness of their 
protoplasm. During the end of the fourth day, aud the early 
part of the fifth, they increase in number, either by division or 
by addition from the surrounding mesoblast, till in an embryo 
of about the middle of the fifth day of incubation, they form 
groups of a considerable size, which present in section the 
appearances seen in fig. 17. The cells seen in this section, 
though they are more numerous than at the time of their first 
appearance, have not appreciably changed their relations to the 
surrounding parts. They are seen to lie surrounded entirely 
by branched mesoblast cells without any connection, either 
with the epithelium of the adjacent glomeruli, or with the walls 
of any blood-vessels. In this isolated condition the suprarenal 
cells remain during the fifth and sixth days, travelling, how- 
ever, gradually towards the mesonephric glomeruli, and at the 
same time increasing in number, and tending to arrange them- 
selves in irregular branched columns, having in section an 
elliptical outline. During the seventh day they attach them- 
VOL, XXV. — NEW SEK. 
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