ON THE SUPRARENAL BODIES OF VEETEBRATA. 187 



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 aad 

 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 or 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, and 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 thorn- 



