The Transformation of the Mexican Axototl. 603 



another species) " in the hottest parts of the United 

 States." " On the Mexican plateau, however, it 

 snows every winter, and if the lake does not actually 

 freeze, its temperature must fall very considerably 

 in the shallowest parts." 



But although this view is not opposed by any 

 theoretical considerations, I still hold it to be in- 

 correct. I doubt whether it is temperature that 

 has brought about the reverse transformation of 

 the Amblystoma into the Axolotl, or which, accord- 

 ing to De Saussure's conception, at the present 

 time prevents the transformation of the Axolotl in 

 the Lake of Mexico. I doubt this because Ambly- 

 stomas are now known from all parts of the United 

 States as far north as New York, a proof that a 

 winter cold considerably greater than that of the 

 Mexican plateau is no hindrance to the metamor- 

 phosis of the Axolotl, and that the genus does not 

 show itself to be in this respect more sensitive than 

 our native genera of Salamandrida. 



The following observations of De Saussure, in 

 which he calls attention to the nature of the 

 Mexican Lake, appear to me to be more worthy of 

 consideration : " The bottom of this lake is 

 shallow, and one passes imperceptibly from the 

 lake into extensive marshy regions before reaching 

 solid ground ; perhaps this circumstance makes 

 the Axolotl incapable of reaching dry land, and 

 prevents the transformation." 



In any case the Lake of Mexico offers very 



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