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W. F. R. 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 in 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 between 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 
