EMBRYOLOGY OF CRYPTOBRANCHUS 551 



Whipple ('06), from a comparative study of the ypsiloid appa- 

 ratus in urodeles reaches the following conclusions: 



(a) ''That forms with lungs but without vestiges of an ypsiloid 

 apparatus, and with no evidence of degeneration in the pelvic 

 region (e.g., Necturus) are neither degenerate forms, nor perma- 

 nent larvae of any of the salamandrina." 



(b) ''That the presence of a functional ypsiloid apparatus 

 in Cryptobranchus indicates that Cryptobranchus lies near the 

 line of descent of the salamandrina." 



In summing up the facts for and against the hypothesis of 

 the phylogenetic relationships of the perennibranchs, derotremes 

 and salamandrina as outlined by Versluys, it seems to me that 

 the arguments in favor of the hypothesis are founded on charac- 

 ters of greater phylogenetic value. In the reptiles and mammals, 

 land forms are always pi-imitive, aquatic forms secondary (Os- 

 born '02). To the writer the evidence seems convincing in favor 

 of a similar view for the recent urodeles. It might be added 

 that pentadactylous limbs, more or less perfectly developed in 

 fossil as well as recent amphibia, were undoubtedlj' produced 

 in connection with terrestrial habits; and it should be emphasized 

 that the forms ancestral to the present-day aquatic urodeles were 

 probably not pui-ely terrestrial, but passed through an aquatic 

 larval stage, as in Branchiosaurus and most of the living sala- 

 manders. 



It remains to consider briefly the phylogenetic value of some 

 of the facts concerning the life cycle of Cryptobranchus that 

 are embodied in the present contribution, and to discuss their 

 bearing on the subjects just treated from a historical point of 

 view. In an investigation thus far confined mainly to the exter- 

 nal features of development, manifestly little more than a begin- 

 ning can be made in such an interpretation. 



The repeated failure of embryological generalizations to solve 

 some of the lai-ger phylogenetic problems led to a widespread 

 reaction against the earlier too sweeping conclusions based on 

 the recapitulation theory. The reproductive processes, while so 

 fundamental, are very plastic, modified in closely related species 

 and even changing somewhat in the same species kept under 



