The Transformation of the Mexican Axolotl. 621 



Axolotl not only requires the proof that Ambly- 

 stomas cannot exist under present conditions in 

 Mexico, but also the further demonstration that at 

 a former period other conditions prevailed there, 

 and these of such a nature as to make the 

 existence of land-salamanders possible. 



With respect to my question, whether we might 

 not perhaps assume that at some post-glacial 

 period the conditions of atmospheric moisture on 

 the high plains of Mexico were essentially different 

 from those at present prevailing, I recollected Dr. 

 v. Frantzius and the above-quoted observation of 

 Humboldt's, 41 who discovered in the neighbour- 

 hood of the Lake of Tezenco (Mexico) distinct 

 evidence of a much higher former level of the 

 water. " All such elevated plains were certainly 

 at a former period so many extensive water-basins, 

 which gradually became filled, and are still filling 

 up with detritus. The evaporation from such 

 large surfaces of water must at that time have 

 caused a very moist atmosphere, favourable to 

 vegetation and adapted for the life of naked 

 Amphibia." 



From this side also my hypothesis thus receives 

 support, and we may assume with some certainty 

 that at the beginning of the diluvial period " the 



61 " Essai politique sur le Royaume de la Nouvelle 

 Espagne," 1805, p. 291. 



M [The expression made use of by the author, viz. " Dilu- 

 vialzeit," would perhaps be more in harmony with the 

 views of English geologists if rendered as the " pluvial period," 



S s 2 



