606 Studies in the Theory of Descent. 



the water, and this alone may have been sufficient 

 to have induced it to acquire the habits of a purely 

 aquatic existence, and thus to revert to the perenni- 

 branchiate or Ichthyodeous form. 



But enough of supposition. We must not com- 

 plain that we are unable from afar to discover with 

 precision the causes which compelled the Axolotl 

 to abandon the Amblystoma stage, as long as we 

 are not able to explain the much nearer cases of 

 reversion in Filippi's and Jullien's Tritons ; never- 

 theless, in these cases also, the causes affecting 

 the whole colony of Tritons must be general, 

 since at least in the case noticed by Filippi the 

 greater majority of the individuals remained in the 

 larval condition. Experiments with Triton larvae 

 could throw greater light upon this subject ; it 

 would have in the first place to be established 

 whether reversion could be artificially induced, and 

 if so, by what influences. 



From the previously mentioned experiments with 

 butterflies, as well as from the results obtained with 

 Axolotls,we should expect that in Tritons, reversion 

 to the Ichthyodeous form would take place if we 

 allowed the inciting cause, viz. the bathing of the 

 gills and of the whole body with water, to act per- 

 sistently, and at the same time withheld that in- 

 influence under whose action the salamander form 

 became developed, viz. the bathing of the gills, 

 the skin, and the surfaces of the lungs with air. 

 Old experiments of this kind are to be met with, 



