148 
W. F. R. WELDON. 
he did not investigate the details of its development. This 
was afterwards done by Emery, 1 with the following re- 
sults : — 
In those Teleostei which he has studied, Professbr Emery 
finds that at an early stage the kidney consists entirely of a 
single pronephric funnel, opening into the pericardium, and 
connected with the segmental duct, which already opens to the 
exterior. Behind this funnel, the segmental duct is surrounded 
by a blastema, derived from the intermediate cell mass, which 
afterwards arranges itself more or less completely into a series 
of solid cords, attaching themselves to the duct (see fig. 20). 
These develop a lumen, and become normal segmental tubules, 
but it is, if I may be allowed the expression, a matter of 
chance, how much of the blastema becomes so transformed 
into kidney tubules, and how much is left as the “ lym- 
phatic ” tissue of Balfour, this “ lymphatic ” tissue remain- 
ing either in the pronephros only, or in both pro- and meso- 
nephros. 
We have here, as it seems to me, an explanation of the 
reason why the suprarenals, while arising from the pronephros 
in Mvxinoids, are mesonephric in origin in the higher Verte- 
brates. The same causes which led to the degeneration of the 
original renal pronephros (causes among which the specialisa- 
tion of the pericardium, and the development of the air-bladder 
and lungs may have played a considerable part) — the same causes 
which led to the establishment of the mesonephros as the chief 
seat of renal secretion may, and indeed must, have rendered 
advantageous the suppression of any glandular organ in the 
pronephric region; and thus, when, in consequence of the change 
of function of the Wolffian duct more and more of the meso- 
nephros became useless as a kidney, it is easy to understand 
how some of its component parts underwent in their turn the 
same change of function as had been undergone by the 
anterior part of the renal organ at an earlier stage in its 
evolution, stages in the completion of this process remaining 
1 ‘Atti dell’ Academia dei Lincei.,’ 1882. 
