372 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA 



be supported by facts, namely, the assumption that the ancestors of the 

 Axolotl had at an earlier time already been Amblystomas. 



We know from Huiviboldt * that the surface of the Lake of Mexico 

 once lay considerably higher than at present, and that in a time com- 

 paratively modern. We knosv, further, that the plateau of Mexico was 

 covered with forest, while now the forest has vanished where the settle- 

 ments of man, especially of the Spaniards, have reached. Now, if one 

 may suppose that somewhere about the diluvial epoch tbe mountain 

 forest extended to the edge of the lake, then still deep and with abrupt 

 shores and containing considerably less salt, we have indicated condi- 

 tions of life not only different essentially from the present ones, but also 

 such as were qViite specially favorable for the shaping of a species of 

 the Salamandrida. 



In the light of all this I believe people will not be able to cast upon 

 ray attempt to explain the exceptional metamorphosis of the Axolotl 

 from the Lake of Mexico the reproach of being too free a flight of fancy. 

 At any rate it is the only possible explanation which can be opposed to 

 that other one which assumes that the occasional transformation of the 

 Axolotl is not reversion, but an effort to advance. And this assumption 

 must, in my estimation, be rejected on purely theoretical grounds by 

 every one who thinks a sudden transformation of species inconceivable, at 

 least when it is joined with adaptations to neiv conditions of life. That as- 

 sumption must be rejected by every one who looks upon adaptations not 

 as the work of magic arising at a stroke, but as the final result of a long 

 succession of natural causes, though separately slight and imperceptible. 



Should my interpretation of the facts be correct, this history of trans- 

 formation would not have a significance so far-reaching as if it could 

 have been taken in favor of heterogeneous creation, namely : in that 

 case, demonstrating the existence of heterogeneous creation, it would 

 have settled the question between that and transmutation. Now, on the 

 contrary, it brings no definite decision, because, strictly taken, the 

 refutation of sudden transformation in one case only proves it as not 

 present for this one case. 



But it is, after all, a contribution to the gradual and complete rejection 

 of such sudden transformation. If one case after another which seemed 

 to speak for heterogeneous creation is proved untenable on that theory, 

 the argument by induction must finally acquire sufficient strength to bo 

 acknowledged as satisfactory. 



If my view of the facts is correct, a few corollaries result from it which 

 here at the close I should like to mention briefly. 



First, a thing that is more external : 



If the Siredon Mexicanus Shaw only assumes the Amblystoma form 

 by occasional reversion, but never reproduces as such, but only as Sire- 

 don, we cannot approve the action of the latest writers on systematic 

 zoology, who simply strike the genus Siredon out of the system, and 



*See Miihleuxiforclt's book already quoted, vol. i. 



