The Transformation of the Mexican Axolotl. 599 



to revert to the Amblystoma form, certainly no 

 greater leap would have been made from a mor- 

 phological point of view, than in the reversion of 

 Triton to the perennibranchiate form, but at the 

 same time the leap would be in another direction, 

 viz. over a long series of generations back to a form 

 which the species had not produced foralong period, 

 and which had to a certain extent become foreign 

 to it. We should thus have here also the grafting 

 of a widely different constitution upon that of the 

 Axolotl, or, if one prefers it, the commingling of 

 two widely different constitutions. 



Of course I am far from wishing to pretend that 

 this " explanation " is exact ; it is nothing more 

 than an attempt to point out the direction in which 

 the causes affecting the reproductive powers in 

 different degrees are to be looked for. A deeper 

 penetration into and special demonstration of the 

 manner in which these causes bring about such 

 results, must be reserved for a future period. For 

 the present it must suffice to have indicated that 

 there is an essential distinction between the two 

 kinds of reversion, and to have made it to some 

 extent comprehensible that this distinction may be 

 the determining impulse with respect to the question 

 of sterility. Perhaps the law here concealed from 

 us may one day be thus formulated : Atavistic 

 individuals lose the power of reproduction the more 

 completely, the greater the number of generations 

 of their ancestors whose ontogeny no longer com- 



