li' 1 Origin of the Suprarenal Bodies of Vertebrates. [Nov. i'7, 



After a time, the dorsal branch becomes separated from the rest, 

 being cut off by numerous small veins, which divide its substance into 

 irregular trabeculie. Its component cells also stain less easily than 

 those of the ventral branch of the glomerular process. These dorsal 

 branches are, as shown by their position, and by their subsequent 

 nnion with processes from the neighbouring sympathetic ganglia, the 

 rudiment of the cortical portion of the suprarenal body, the ventral 

 processes forming the longitudinal network of the testis, already 

 described by Braun. 



The close contact which exists, in the later stages of development, 

 between the suprarenal rudiment and the various blood-vessels which 

 run through it, has led previous observers to assume that the blastema 

 itself originates by proliferation of the walls of those vessels. The 

 fact that the glomernlar processes already mentioned may be easily 

 recognised before the existence of these vascular branches, together 

 with the great clearness and distinctness of the endothelium of the 

 latter, which may always be seen as a sharply defined layer lying 

 on the suprarenal substance, completely negative this view. 



The later behaviour of the cortical blastema, and its union with the 

 sympathetic, has been correctly described by Braun. 



In the chick the development is, as might be expected, much modi- 

 fied. About the end of the fifth day numbers of large, rounded, 

 deeply staining cells appear in the tissue between the vena cava and 

 the mesonephros. These cells unite, during the sixth and seventh 

 days, into clusters and finally into chains which acquire, on the eighth 

 day, a connexion with the epithelium of adjacent glomeruli. After 

 this they behave in a manner practically identical with that of the 

 corresponding cords in the lizard. 



As in the lizard, so in the chick, the cells in question are from the 

 first so perfectly distinct from the walls of the adjacent vessels that 

 they can by no possibility be supposed to have been budded off from 

 them. 



In Pristiuru*, the suprarenals are, as is well known, segmentally 

 arranged along the dorsal wall of the cardinal veins. Balfour 

 describes their cortical tissue as arising from an impaired rod of meso- 

 blast, lying at the root of the mesentery. As to the origin of the 

 rod itself, he says nothing. Its actual origin I believe to be this : 

 each segmental tube, before the formation of a glomerulus, gives off a 

 hollow bud, towards the root of the mesentery, so that it becomes 

 Y-shaped, the foot of the T representing the peritoneal funnel, one 

 limb being the suprarenal bud, aud the other the connexion with the 

 segmental duct. Almost immediately after its formation, the internal 

 limb of the Y breaks off, and fuses with its fellows to form the 

 unpaired rod at the root of the mesentery of which Balfour speaks. 



The results of these observations we may sum up by saying that all 



