ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 357 



To be sure 1 could have perceived the great difference between the 

 two stages of development from the anatomical data long familiar to 

 me which Dumdril had given on the structure of his Amblystomas; 

 but the reading over of many statements in detail gives no living pict- 

 ure. At any rate the sight of the living animal first brought me to the 

 ^'ousciousness how comprehensive is the change we have to do with 

 here; that by no means does it merely concern those parts which are 

 directly affected by the alteration in the mode of life, but that most, 

 if not all, parts of the animal undergo a transformation, which can be 

 very well explained in part as the morphological adaptation to new con- 

 ditions of life, in part as consequences of these adaptations (correlative 

 changes), but cannot by any possibility be explained in a word as the sud- 

 denly appearing effect of these changed conditions of life. Such at least is 

 my view, according to which a sudden development of the species, such 

 as must have taken place here, is quite inconceivable. I willingly ac- 

 knowledge that a few years ago the question whether such sudden de- 

 velopment occurs was still an open one for me, but since then my invest- 

 igations have kept urging me to the conviction that it does not occur at 

 all, as I shall show in another i)lace. Here 1 have to confine myself to 

 the examination of this individual case; a case which appears to me — 

 as was above intimated — quite peculiarly suited to shed light decisively 

 upon the great alternative, about which at the present moment the war 

 of opinions is centered, in regard to the doctrine of descent. 



I may well assume that hitherto it has been with most students in 

 regard to the metamorphosis of the Axolotl very much as with myself; 

 it did not come to their consciousness hoic far the transformation goes ; 

 and so it may need to be made plain that the theoretical importance of 

 the case and its value as a basis of inference was not properly emphasized 

 by either side. But it is evidently a case of quite unusual significance 

 for the principles involved. I believe it may be easily shown that the 

 hitherto pretty generally admitted explanation of the history of the 

 Paris Axolotl's transformation includes at the same time the recogni- 

 tion of a very far-reaching principle, namely: if this explanation were 

 the correct one, then in my judgment would be at the same time demon- 

 strated as correct the opinion of those who, like Kolliker, Askenast, 

 NAaELi, and among the philosophers Hartmann and Huber, would 

 refer the transmutation of the species in the first instance to a motive 

 power dwelling within the organisms, to an active, i. e. spontaneous, 

 *'law of development," a ''])riuciple of perfection," or, as I should pre- 

 fer to name it, a phyletic vital energy., in contrast to the exactly corre- 

 sponding vital energy of the so-called "philosopher domain" in the 

 nature of ontogenesis. 



If, namely, the Axolotls that have become Ambly stomas are to be taken 

 as individuals which, stimulated by external influences, have hastened 

 on in advance of the remaining individuals in their phyletic develop- 

 ment, then this advance can only be placed to the account of a phy- 



