ON THE SUPRARENAL BODIES OP VERTEBRATA. 183 



vessels (diagrammetrically indicated by shading). The epithe- 

 lium of the glomerulus is everywhere, except on its inner side, 

 formed of a single layer of cells, which are much flatter than 

 in the preceding stage, but on the inner side the cells pass, 

 as before, without any definite line of demarcation, into the 

 suprarenal blastema, which is still composed of a compact mass 

 of polygonal cells, without any distinction being visible between 

 the part which is going to form suprarenal body and that 

 which is going to form a seminiferous tubule. In this section 

 the distinction between the endothelial cells of the various 

 blood-vessels and the tissues surrounding them is even better 

 marked than in the one last described. 



The appearances which I have attempted to describe are seen 

 first in the more anterior, then in the hinder glomeruli of all 

 that region of the mesonephros which is coextensive with the 

 generative ridge, and in one or two glomeruli in front of it. 



The blastema which I have described grows, in the suc- 

 ceeding stages, in two directions : dorsalwards between the 

 cardinal vein (or vena cava) and the tubules of the mesone- 

 phros, and ventralwards into the prominence of the Wolffian 

 ridge. In such a section as that shown in fig. 3, for example, 

 which is taken from the posterior part of the mesonephros of 

 an embryo of 8 mm., two distinct regions may now be distin- 

 guished, a region (s. r. h.) dorsal to the point of origin from 

 the glomerulus, the cells composing which will go to form the 

 suprarenal, and a region (s. sir.') going from the glomerulus 

 ventralwards into the generative ridge, which is the rudiment 

 of the testicular network. No histological difference can as 

 yet be detected between the one region and the other, the 

 whole blastema being composed of a mass of polygonal cells 

 with rounded nuclei, the characters of which are everywhere 

 identical. 



In an embryo of 10 mm. (figs. 4 and 5), a slight dis- 

 tinction between the two parts is for the first time apparent, 

 though the histological characters of adult suprarenal cells are 

 not acquired for some time. Of the two sections figured, that 

 shown in fig. 4 is taken in front of the Wolffian ridge ; in it. 



