356 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 



form. No oue can o'^ject to this statement ; while the other proposi- 

 tiou, either expressed or taeitly held by all authors, includes a theory 

 which I regard as incorrect. That i)roposition is : The Mexican Axolotl 

 has remained upon a lower phyletic stage of development. 



All zoologists who have expressed themselves on the transformation 

 of the Mexican Axolotl, and who are not, like its first observer, still 

 attached to Cuvier's views ou the immutability of species, took up the 

 matter as if here was a species which through some sort of special cir- 

 cumstances had remained behind on a lower stage of development, and 

 was now stimulated by some sort of influences to its advance to a 

 higher stage. 



For a long time also I did not believe that the thing could be other- 

 wise understood, little as I was able to bring all the phenomena into 

 harmony with this view. Thus in 1872 I used the following expres- 

 sions :* "Why should not a sudden change in all the relations of life 

 (the removal from Mexico to Paris) have had a direct influence upon 

 the organism of the Axolotl, so that he suddenly attained a higher stage 

 of development, which many of his kindred species have long since 

 attained, which evidently lies in the nature of his organization, and 

 which perchance he also would have reached in his native haunts, though 

 at a later period ? Or would it be too much to suppose that by the 

 sudden transportation from 8,000 feet above the sea-level (the Mexican 

 highland) to the altitude of Paris, the organs of respiration had re- 

 ceived a shock which just brought them to the change already close at 

 hand ? So in all probability we have to do with a direct effect from 

 altered conditions of life." 



That the purport of the lost sentence must also be held true to-day 

 follows as a matter of course from the experiments communicated above, 

 which surely prove that by the application of definite external influences 

 we have to a certain extent it in our power to call forth the transforma- 

 tion. Just in that fact lies the new light which these experiments have 

 brought. 



But must we also understand the phenomenon in the manner above 

 indicated — that is to say, as a phyletic onivard development of the specie.'';, 

 appearing suddenly and in a measure resulting from a shoclcf I believe 

 not. What first perplexed me in regard to this view was the sight of 

 my living Amblystomas reared from the l.arvse of the Axolotl. These 

 creatures by no means show a variation from the Axolotl in single traits 

 merely, but they are distinguished from it in their entire habit; they 

 differ somewhat in all parts; although slightly in many, in others quite 

 decidedly; in short they have become entirely different animals. Corre- 

 sponding to this they also live quite differently; no longer go into the 

 water, but prefer in the daytime to keep hidden in the damp moss of 

 their prison, and at night come forth to seek their food on the dry laud, 



*"Ueberdeu Eiufluss der Isolining auf die Artbildung" (On the Influeuce of Isolation 

 upon the Formation of Species), Leipsic, 187:2, p. 33. 



