370 ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 



or — according to De Saussure's explanation — which at the present 

 hinders the transformation of the Axolotl in the Lake of Mexico. This 

 is the reason for my doubt : From all portions of the United States to the 

 northward of New York Amblystomas have been collected ; a proof that 

 even a much greater degree of winter cold than that found on the 

 plateau of Mexico is no hinderance for the transformation of the 

 Axolotl ; that the genus does not prove more sensitive in this respect 

 than our native genera of Salamandrida. 



More consideration seems to me to be deserved by the following 

 remarks of De Saussuke, in which he points out the character of the 

 Mexican lake : " The bottom of this lake is flat, so that one comes im- 

 perceptibly from the lake to wide, swampy regions before he reaches 

 firm ground. Perhaps this condition makes the Axolotl unable to get 

 to the dry land, and so hinders the transformation." 



At any rate the Lake of Mexico o£fer§ very peculiar conditions of life 

 for an ami)hibious animal. My esteemed friend, Dr. Y. Frantzius, 

 called my attention to it that this lake, like many others also of the 

 Mexican lakes, is brackish. At the time of the conquest of Mexico 

 by Ferdinand Cortez this circumstance caused the final surrender, as 

 the Spaniards cut off the water from the besieged and the lake water 

 is not drinkable. The old Mexicans had already built conduits from 

 the distant mountains, and at the present day the city is still depend- 

 ent on the water brought in by aqueducts. 



l!^ow, this saltness, in and for itself, could be no cause for the falling 

 back to the Perennibranchiate form, but might be such a cause, in 

 connection with other peculiarities of the lake. The shallowest part of 

 the lake is the eastern, and only in this part does the Axolotl live. In the 

 winter violent storms from the east blow regularly and persistently, which 

 come down from the mountains and drive the water before them so power- 

 fully that it rises in the western part of the lake and frequently causes 

 overflows there, while from the flat eastern shore the bottom is laid com- 

 pletely dry for 2,000 feet.* i!^ow if one puts together these two peculi- 

 arities, the salt and the periodical drying of a part of the lake-bottom by 

 continued winds, he gets at any rate conditions of life for the Axolotl 

 such as can be found in very few other places. To be sure, one might 

 attempt to turn them to use just in an opposite sense, unfavorable to my 

 theory, for the withdrawing of the water from a great part of the lake 

 bottom ought — so might one think — rather to make easier the animal's 

 transition to living on the land ; yes, just compel it thereto. But one for- 

 gets, however, that the bared lake-bottom is a sterile iilain^ without food 

 and without hiding-place ; above all, without vegetation ; and further, 

 that through the pretty considerable saltness of the water (specific 

 gravity, 1.0215) all the surface laid dry must be covered with a crust of 

 salt, a condition which will make feeding on the land just impossible. 



* Miiblenpfordt, A^ersucli einer getreuen Schilderung der Republik Meijco, Hanover, 

 1844, ii, p. 252 (Attempt at a true Picture of the Republic of Mexico). 



