574 Studies in the Theory of Descent. 



of the metamorphosis of Axolotl have, like myself, 

 not been hitherto aware of the extent of the 

 transformation, and it may thus be explained why 

 the theoretical bearings of the case have on all 

 sides been incorrectly conceived. We have here 

 obviously a quite extraordinary case of the first 

 order of importance. I believe that it can easily 

 be shown that the explanation of the history of the 

 metamorphosis of the Paris Axolotl which has 

 hitherto been pretty generally accepted, necessarily 

 comprises a very far-reaching principle. If this 

 interpretation is correct, then in my opinion must 

 also hold good the ideas of those who, like Kolliker, 

 Askenasy, Nageli, and, among the philosophers, 

 Hartmann and Huber, would refer the transforma- 

 tion of species in the first instance to a power 

 innate in the organism, to an active, i.e. a self- 

 urging "law of development" a phyletic vital 

 force. 



Thus, if the Axolotls transformed into Amblys- 

 tomas are regarded as individuals which, impelled 

 by external influences, have anticipated the phyletic 

 development of the others, then tnis advance can 

 only be ascribed to a phyletic vital force, since the 

 transformation is sudden, and leaves no time for 

 gradual adaptation in the course of generations. 

 The indirect influence of the external conditions 

 of life, i. e. natural selection, is thus excluded from 

 the beginning. But the direct action of the 

 changed conditions of life by no means furnishes 



