632 Studies in the Theory of Descent. 



the recurrence of the rainy season, when they 

 would hasten back into the water and would there 

 live as a species of Triton. 



Now one might feel inclined to ask why the 

 species of the great Mexican lake has not also 

 taken to this mode of life. To this it may be 

 simply replied that the water of this lake never 

 dries up, and that the Axolotls have thus never 

 been reduced to the alternative of undergoing 

 metamorphosis or of perishing. If therefore the 

 conditions of existence in water were more favour- 

 able than on land, the tendency to abandon meta- 

 morphosis would increase from generation to 

 generation, and the deportment at present ob- 

 served would finally result, t. e. propagation would 

 take place exclusively in the Axolotl state. As 

 has already been mentioned above, the latest 

 observations of Velasco furnish further confirma- 

 tion that the Axolotl of the great lake is never 

 met with in the Amblystoma condition, " although 

 it (the Axolotl) is brought daily from Mexico 

 into the market throughout the whole year." I 

 should not however regard it as a refutation of 

 my view if prolonged investigation should show 

 that this species also (Siredon Humboldtii) oc- 

 casionally developed into an Amblystoma ; on the 

 contrary, it would not at all surprise me. if such 

 cases of reversion occurred in Mexico as well as 

 in Europe. The fact that an immense majority of 

 the Amphibians propagate in the Axolotl state 



