186 W. F. E. WELDON. 



SO coalesced with those in front and behind that an interverte- 

 bral section, such as that shown in fig. 15, still passes through 

 them. 



One feature of the sections of this age, which I do not 

 understand completely, is the shifting of the position, with 

 regard to the segmental funnel, of the point of attachment of 

 the suprarenal outgrowth ; while in the preceding stage (see 

 fig. 12) the outgrowth was external to the primitive ova, open- 

 ing distinctly into the segmental funnel, it is now attached to 

 the peritoneal epithelium at the root of the mesentery internal 

 to the primitive ova. While I am unable to account for 

 this apparent change of position, I see no reason for doubt- 

 ing the identity of the structure I have called s. v. in figs. 14 

 and 15 with that similarly named iu the preceding figures. 



In the next stage, finally, which is a young embryo of 

 Balfour^s Stage IV, we find (fig. 16) the unpaired rod of meso- 

 blast described by him lying at the root of the mesentery, 

 but still attached segmentally (see the left hand side of the 

 figure) to the segmental funnel. 



I have unfortunately no stage intermediate betweea this 

 and the stage last described, but it seems obvious that the 

 unpaired blastema existing at this stage must be produced by 

 the fusion of the paired outgrowths of the earlier stages. 



An important point with regard to this blastema in Pris- 

 tiurus, which has apparently been overlooked by Balfour, is 

 that it extends throughout the whole length of the mesonephros. 



It is well known that in an adult Elasmobranch there are 

 two sets of suprarenal bodies : one a series of paired, more or 

 less regularly segmental bodies, attached to the dorsal wall of 

 the cardinal vein on each side in the mesonephric region, and 

 the other one unpaired, median body, lying between the two 

 halves of the metanephros. 



Balfour was of opinion that the bodies of the anterior set, 

 though they show in the adult a division into cortical and 

 nervous positions as distinct as that which exists in the supra- 

 renals of higher Vertebrates, were yet derived entirely from 

 sympathetic ganglia. The presence, in the anterior end of the 



