The Transformation of the Mexican Axolotl. 60 1 



form, I must admit that I can only offer a con- 

 jectural reply, having but a conditional value so 

 long as it is not supported by a precise knowledge 

 of the conditions there obtaining, and of the habits 

 both of the Axototl and of the Amblystoma. 



It may be supposed generally that reversion is 

 brought about by the same external conditions as 

 those which formerly produced the perennibran- 

 chiate stage. This supposition is in the first place 

 supported by the experiments here recorded, since 

 it is evidently the inducement to aerial respiration 

 which causes the young Axolotl to revert to the 

 Amblystoma form, i.e. the inciting cause under 

 whose domineering influence the Amblystoma form 

 must have arisen. 



Here again the case is quite similar to that of 

 seasonally dimorphic butterflies. Reversion of 

 the summer brood to the winter form is there most 

 easily caused by the action of cold, i.e. by the 

 same influence as that under whose sway the winter 

 form was developed. 



We know indeed that reversion may also arise 

 by the crossing of races and species, and I have 

 attempted to show that reversion in butterflies may 

 also be brought about by other influences than 

 cold ; but still the most probable supposition 

 obviously is, that reversion would be caused by the 

 persistent action of the same influences as those 

 which in a certain sense created the perennibran- 

 chiate form. That the latter was produced under 



