The Transformation of the Mexican Axototl. 631 



(Tritons), which remain in the water at least during 

 the whole period of reproduction. These also 

 leave the water later, and, like the land-salamander, 

 seek concealment in the earth. They have this 

 habit also in those districts which possess a very 

 dry atmosphere ; and especially in the Engadine, 

 where I first conceived the idea of taking into 

 account the dryness of the air, I found in the 

 pools at the end of August and the beginning of 

 September only larvae of Tritons. The older 

 Amphibians must therefore have been on the land, 

 presumably in their places of winter concealment. 



From what we have hitherto learnt from Senor 

 Velasco, the mode of life of Amblystoma Tigrinum 

 must resemble that of our Tritons, although its 

 structure is that of a land-salamander. I would 

 thus offer the following explanation of the facts at 

 present known : Owing to the periodic drying up 

 of the lake of Santa Isabel, the Siredon Tigrinus 

 would be again compelled to undergo meta- 

 morphosis. Whether this was formerly entirely 

 abandoned, orwhether it always occurred in solitary 

 individuals, is almost immaterial ; in any case the 

 habit of metamorphosis must have been very 

 rapidly acquired through natural selection, and 

 must have again become general, if the faculty 

 was only present in the species, although latent. 

 Through the dryness of the air, the Amblystomas 

 that had taken to the land would be compelled to 

 bury themselves at once, and to remain asleep till 



