ON CHANGE OF MEXICAN AXOLOTL TO AN AMBLYSTOMA. 363 



Accordiug to my view tliis would be a case of reversion of the Triton 

 to thephyletic stage lying next behind it, that is, the Perennibranchiate stage; 

 and ill this case most zoologists who stand at all upou the footing 

 of the doctrine of descent will agree with my view. I at least would 

 count it a profitless playing with words if any one should speak here of 

 larval reproduction and believe he had thereby explained anything. In 

 any event the animal becomes sexually mature in the condition in which 

 it first appears as a larva. But we first get an insight into the nature of 

 this phenomenon by the reflection that tbis so called "sexually mature 

 larva" has precisely the structure which the preceding phyletic stage 

 of the species must have possessd ; that therefore we have a reversion 

 of the individual to the older phyletic stage of the species. I es- 

 teem it an error when DmiERiL puts this case of the Triton in par- 

 allel with the genuine larval reproduction of Wagner's Gecidomyia 

 larvae. There it i3 certainly not reverision to an older phyletic stage 

 which makes tbelarvte capable of reproduction ; for these larvce present 

 no older phyletic stage of the species, but must have arisen at the same time 

 icith the species in its present fjrm. The vast difference in tbe structure 

 of the larva and the fly is not explained by assuming that the latter 

 has arisen from the former as from a finished given quantity, but by 

 this, that both at the same time have adapted themselves to conditions 

 of life further from each other.* Eegarded phyleticall}", these larvae are 

 not at all a necessary point of transit for the origin of the fly. They 

 could also be built quite otherwise, without the form of the fly needing 

 to be likewise changed ; for the stages of insect transformation vary 

 Independently of each other, corresponding to the conditions of life to 

 which they are subjected, and exert no influence upon each other, or 

 only a very slight one, in the determination of form, as I shall attempt 

 to demonstrate in another place. At any rate, "the ability of these 

 larvae (the Cecidomyia) to multiply asexually has first been acquired as 

 a secondary matter, as already follows from the fact that there are 

 numerous species of the same genus of flies which do not feed their 

 young." " In the form which they possess to-day they can never have 

 played the part of the final stage of ontogenesis, and therefore also 

 cannot have possessed at a former time the power of sexual repro- 

 duction. t In short, we have to do here with genuine larval reproduction, 

 but in the Tritons with reversion to an older phyletic stage. 



Isor can I agree with my friend Haeckel, when he designates the 

 reversion of the Tritons as "adaptation to continued life in the water." | 



One would only be able to speak of " adaptation " in this case by tak- 

 ing the word in a sense quite difl'erent from that with which Darwin 



• Compare, also, Lubbock, Oa the Origin and Metamorphoses of Insects. Londou, 

 1874. 



t Seo my paper "Ueber den Saison-Dimorphismus der Schmetteiiinge," Leipsic, 

 1675, p. GO. 



t See Haeckel's Anthropogeuie, p. 449. 



