586 Studies in the Theory of Descent. 



should at least consider it to be a useless play 

 upon words did we here speak of larval repro- 

 duction, and thereby believe that we had explained 

 something. The animal certainly becomes sexually 

 mature in the same condition as that in which it first 

 appears as a larva, but we first get an insight into 

 the nature of this process by considering that this 

 so-called " sexually mature larva" has the precise 

 structure which must have been possessed by the 

 preceding phyletic stage of the species, and that 

 an individual reversion to the older phyletic stage 

 of the species is consequently before us. I main- 

 tain that DumeVil is in error in regarding this case 

 of the Triton as parallel with the true larval re- 

 production of Wagner's Cecidomyia larva. In 

 this last case it is certainly not reversion to an 

 older phyletic stage that confers the power of 

 reproduction upon the larvae, since the latter do 

 not represent an older phyletic stage of the 

 species, but must have arisen contemporaneously 

 with this last stage. The enormous structural 

 difference between the larvae and the imagines is 

 not explained by the latter having arisen from the 

 former supplementarily as a finished production, 

 but by both having been contemporaneously 

 adapted tv O continually diverging conditions of 

 life. 21 Considered phyletically, these larvae are by 

 no means necessarily transitional to the origination 



" See also Lubbo. c k " On the Origin and Metamorphoses of 

 Insects," London, 187 4. 



