596 Studies in the Theory of Descent. 



.Darwin 33 finds the proximate causes of sterility 

 in the first place in the action of widely diverging 

 conditions of life, and in the next place in the 

 crossing of individuals widely different in constitu- 

 tion. Now it is certainly deviating conditions of 

 life which lead to the metamorphosis of the Axolotl, 

 and from this point of view it cannot be surprising 

 if we find those individuals sterile which show 

 themselves so especially affected by these changed 

 conditions as to revert to the salamander form. 



By this it is not in any way meant to be asserted 

 that reversion is invariably accompanied by sterility, 

 and one cannot raise as an objection to my inter- 

 pretation of the metamorphosis of the Axolotl, that 

 a reproductive colony of Axolotls could never have 

 arisen by reversion. On the contrary, Jullien's 

 egg-depositing female Triton-larvae show that also 

 with reversion the power of reproduction may be 

 completely preserved. 34 From the above-mentioned 



" Origin of Species, 6th ed. p. 252. 



M In plants also reversion forms show sterility in different 

 degrees. Mr. Darwin has called my attention to the fact that 

 the peloric (symmetrical) flowers which occasionally appear as 

 atavistic forms in Corydalis solida are partly sterile and partly 

 fertile. That in other causes of sterility, and above all by 

 bastardizing, the reproductive power is lost in the most varying 

 degrees, has been known since the celebrated observations of 

 Kolreuter and Gartner. [Eng. ed. An Orchid (Catasetum 

 tridentatuni) has the sexes separate, and the male flowers 

 (Afyanthus barbatus} differ considerably from the female 

 (Monachanthus viridis) ; besides these, there occurs a form 

 with bisexual flowers which must be considered as a reversion 



