190 W. F. B. WELDON. 



he did not investigate the details of its development. This 

 was afterwards done by Emery/ with the following re- 

 sults : — 



In those Teleostei which he has studied, Professor 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. 8) . 

 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 Myxinoids, 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 



' 'Atti dell' Accademia dei Lincei.,' 1882. 



