626 Studies in the Theory of Descent. 



and the gap thus arising in the formerly present 

 cavum inter ma xillare would become filled with 

 connective tissue. 



While the German edition of this work was 

 going through the press I obtained, through the 

 kindness of my friend Dr. Emil Bessels of 

 Washington, the Mexican memoir upon the new 

 Axolotl, 56 which even in Mexico regularly, or at 

 least in many cases, becomes developed into the 

 Amblystoma form. 



The facts are briefly as follows : The small 

 Lake of Santa Isabel is some hours' journey from 

 the Mexican capital. In this lake there lives a 

 species of Axolotl which had hitherto remained 

 unknown, and was described by Senor Velasco as 

 Siredon Tigrinus. This species propagates itself 

 indeed in the Axolotl state, but in many cases it 

 becomes transformed into Amblystoma and takes 

 to the land. Although propagation in the Ambly- 

 stoma condition was not observed, it can hardly be 

 doubted that it also propagates in this form. 



At first sight these facts appear to refute my 

 hypothesis, that the extreme dryness of the air of 

 the Mexican plateau precludes the existence of 

 land Amphibia. Nevertheless I do not abandon 

 this hypothesis for the former one, since a closer 

 study of the data furnished by Velasco confirms 

 rather than refutes my supposition. 



Velasco expressly corroborates the statement 

 M See note 2, p. 566. 



