MORPHOLOGY OF CYCLOSTOMATA. 399 



Bufo, and Rana. His accounts confirm, as a whole, those given 

 by RÜCKERT for Sehichia above referred to, but differ some- 

 what from those of most other authors who have worked on 

 Amphibian pronephros. Mollier states as follows : " Wir sehen 

 hier ebenfalls zuerst eine solide, von dem Mesoblast ausgehende 

 Anlage, deren Structur anfänglich schwer zu erkennen ist und 

 erst mit dem Hohlwerden, wie bei den Selachiern, klar hervor- 

 tritt. Dann linden wir, dass hier zwei resp. drei getrennte 

 Cimälclien vorhanden sind, die von den Somiten in conver- 

 genter Kichtung ausgehen und erst nachträglich untereinander 

 vereinigen zu einem Längscanal, von dem aus die Vornierent- 

 richter in die Leibeshöhle führen " [loco cit., p. 229)/^ The 

 author derives in this wise the pronephric tubules, exactly as 

 in the case of Pctromyzon, from the segmented part of the 

 mesoblast only. 



Mollier's accounts are for the most part in close accord 

 with the results given by Field ('91, p. 282), who, one year 

 later independently of Mollier, began with Anura, and 

 extended the wT)rk over Urodele Amphibia. In one point, their 

 results differ Avidel y ; but " the difference is," it seems to Field, 

 " apparent rather than real." According to Mollier, the 

 nephrostomes communicate with the cavity of the myotome, the 

 myocœlome of van Wyhe ; this is denied by Field, who believes 

 that *' the pronephric tubules have to do with the ventral seg- 

 ment of the mesoderm " {loco cit., p. 283). It seems to me 

 that this ** ventral segment of the mesoderm " corresponds to the 

 pronephrotome of van Wyhe in Selachia or to " I'extreme interne 

 de la plaque latérale secondaire " of Swaen and Brächet in 



1) It seems that tlie earliest traces of the pronephros are perceived in an embryo 

 vounsrer than that with 7 somites. 



