The pronephros of Chrysemys margiiiata. 63 



not from protovertebra or neplirotome. Felix gives Eabl's version 

 thus: "Jede Verdickung stellt die Anlage eines Hauptkanälchens dar; 

 da die einzelnen Ursegmente unmittelbar aufeinander folgen und 

 durch keinen irgendwie in Betracht kommenden Zwischenraum von- 

 einander getrennt sind, so bilden die Vorwölbungen der einzelnen 

 Segmente einen kontinuierlichen Wulst, den Vornierenwulst" (solid 

 cell-knob Balfour, 1878). 



v. WiJHE (1889) says that in Pristiurus the duct and the tubules 

 are formed together (in continuity) in the mesoderm, though Rabl (1896) 

 practically refutes this. 



With regard to the Amphibia Felix quotes as follows: 

 "Zunächst w^ird der Vornierenwulst gebildet, eine kontinuierliche, 

 solide Verdickung des Mesoderms, welche sich bei allen genau unter- 

 suchten Batrachiern gleichmäßig über mehrere Segmente erstreckt, 

 auch über solche, in welchen sich später nur der Harnleiter ausbildet 

 (MoLLiEE, 1890, Field, 1891)." 



As regards the Teleostei the description of Felix is quite 

 different to anything found in other Vertebrates, and although the 

 Teleosts are very specialized I am not inclined to agree that Felix's 

 interpretation is the true one. The objections to his interpretation are: 



1. The rudiment of the pronephros (in a trout embryo 26 days 

 old) is stated to arise at a time before somatic and splanchnic layers 

 are apparently differentiated. 



2. The so-called rudiment is found in a different region to that 

 in which the development of the pronephros in other Vertebrates 

 occurs. 



Thus Felix says: "Die einzelnen Kanälchen sind nicht dorsal- 

 wärts gegen das Ektoderm, sondern median- und ein wenig ventral- 

 wärts gerichtet; sie erscheinen infolgedessen als direkte Fortsetzung- 

 der Seitenplatte, sowohl der Somato- als der Splanchnopleura." 



3. The origin of the pronephric rudiment from both somatic 

 and splanchnic mesoderm, instead of from somatic mesoderm onl}^, is 

 again quite unknown in other Vertebrates. 



4. In Felix's (30) figs. 67b and c, 68 and 70 the term 

 "primäre Vornierenfalte" is given to structures which are not 

 homologous, the term being used in the earlier figures for what 

 appears to be the intermediate cell mass. 



Is it not more probable that the "primary pronephric fold" of 

 Felix, — which is, from the first, an unsegmented continuous 



