7,2,6 LEPIDOPTERA 



and F. inarce/Jus. It is uncertain how many generations there 

 may he in one year of this species, as the length of the life- 

 cycle varies greatly according to circumstances. But in West 

 Virginia all the hutterflies of this species that emerge from the 

 chrysalis hefore tlie middle of April are the form mtrrcelh's ; 

 those produced between the middle of April and the end of May 

 are telamonicles ; while those that appear after this are ajao\ 

 P. fchimonuh's is not, however, the offspring oV/itarcr/lt/s, for both 

 iorms emerge from pupae tliat have passed through the winter 

 (and are the offspring of nj'ax), those that emerge early being 

 marcel/ i(>i, those that appear later telamonidrs. 



In various parts of Asia and Africa the butterflies produced 

 during the wet season differ more or less markedly from those of 

 the same species produced during the dry season. These are 

 called " wet " and " dry season " forms. Their aetiology has not 

 been investigated, this discovery being comparatively recent. 



Turning to the early life we find that some larvae vary in 

 colour, and that this variation is sometimes of a definite char- 

 acter, the larva being one of two different colours — green or 

 brown. In other cases the variation of the species is less 

 definitely dimorphic, a considerable range of variation being 

 exhibited by the species. In tracing the life-liistories of Lepi- 

 dopterous larvae it is not rare to find species in which the larva 

 abruptly changes its form and colour in the middle of its life, 

 and so completely that no one would believe the identity of the 

 individual in the twt) successive conditions had it not been 

 shown Ijy direct oljservation ; in these cases the change in 

 apYJearance is usually associated with a change in habits, the 

 larva being, perhaps, a miner in leaves in its first stages, and an 

 external feeder sul)Sequently. In tlie case of the larval variation 

 we have alluded to abo\e, it is understood that there is no 

 marked change of habits. Poulton lias shown ^ that it is not 

 infrecjuent for some of these latter kinds of variable larvae tn 

 chanoe colour durino; life, and he considers that light or conditions 

 of illumination, that he speaks of as " phytoscopic," are the in- 

 ducing causes. Great difference is, however, exhibited according 

 to species, some variable species not being so amenable to these 

 influences as others are. In dimorphic forms the change was 

 observed to take place at a moult, the larva changing its skin 



^ Trails, cnt. Soc. Loiidon, 1892, p. 293, etc. 



