59 2 Studies in the Theory of Descent. 



as shown by anatomical investigation, with well 

 " developed sexual organs," the ovaria especially 

 being distended with eggs. 



It is thus established that species which long 

 ago reached the salamander stage in phyletic 

 development, may occasionally degenerate to the 

 perenni branchiate stage. This fact obviously 

 makes my conception of the Axolotl as a reversion 

 form appear much less paradoxical indeed, the 

 cases of reversion in Triton are precisely analagous 

 to the process which I suppose to have taken 

 place in the Axolotl. We have only to substitute 

 Amblystomas for Tritons, to imagine the pool in 

 which De Filippi found his "sexually mature Triton 

 larvae " enlarged to the size of the Lake of Mexico, 

 and to conceive the unknown, and perhaps here 

 transitory, causes of the reversion to be perma- 

 nent, and we have all that is necessary, so far as 

 we at present know, for the restoration of the 

 Axolotl ; we obtain a perennibranchiate population 

 of the lake. 



It has not yet been determined whether the 

 perennibranchiate form of the Triton actually pre- 

 vailed permanently in De Filippi's pool, since, so 

 far as I know, this has not since been examined. 



Let us, however, assume for an instant that this 

 is really the case, and that there exists at that 

 spot a colony of sexually reproductive perenni- 

 branchiate Tritons : should we wonder if a true 

 Triton occasionally appeared among their progeny, 



