The Transformation of the Mexican AxolotL 595 



theory of reversion actually explains the sterility, 

 but it is at least not directly opposed to it. Mere 

 reversion forms may die off without propagating 

 themselves ; but a new form called forth by the 

 action of a phyletic vital force should not be sterile, 

 because this is the precise " aim " which the vital 

 force had in view. The conception of a vital force 

 comprises that of teleology. 



The sterility of Amblystoma moreover, although 

 not completely explicable from our standpoint, can 

 be shown to be a phenomenon not entirely isolated. 

 In the above mentioned case of Lissotriton Punc- 

 futus, the female " larvae " were certainly sexually 

 mature and laid eggs, but the males of the same 

 period contained in their testicles no fully developed 

 spermatozoa. 



Other cases of this kind are unknown to me ; 

 at the time when I made the experiments with 

 butterflies already recorded (see the first essay), 

 this point of view was remote, and I therefore 

 neglected to examine the artificially bred reversion 

 forms with respect to their organs of reproduction. 

 But general considerations lead to the supposition 

 that atavistic forms may easily remain sterile. 



Amblystomas are therefore not absolutely, but indeed relatively 

 sterile. Whilst the Axolotl propagates regularly and freely every 

 year, this occurs with the Amblystoma but rarely and sparsely. 

 The degree of their sterility can only be approximately estab- 

 lished when we know the number of Amblystomas that have 

 since been kept in the Jardin des Plantes. Unfortunately 

 nothing has been said with respect to this.] 



