THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. 69 



collected in the open air), produced three females, measuring 36-39 mm., 

 after a larval stage of 68-87, and a pupal of 15-20 days. Callimorpka 

 dominula var. romanovitf , of 59 mm. and C. var. persona $ of 55 mm., 

 gave rise, after 65-71 days of larval feeding and 14-19 days in the 

 pupal stage, to a form measuring only 35-38 mm. across the wings, in 

 more than a dozen examples. 



Although in the following experiments no hybernation of the larvae 

 occurred, yet, in contrast to the instances just given, individuals of 

 A. fasciata were reared from eggs of the same pair as above, after 

 142-163 days of larval, and 25-31 days of pupal, existence, which 

 measured 55-57 mm. in expanse ; and eggs of Dendrolimus pini (male 

 59 mm. and female 74 mm.), yielded descendants expanding 65-68 

 mm. in the male, and 84-86 mm. in the female, after 150-172 days of 

 larval feeding and 25-37 days in the pupal condition. 



In tropical countries where there is less marked difference in the 

 temperature at various seasons, but where there is a marked difference 

 in the rainfall, i.e., in countries where the seasons are known as 

 " wet " and " dry," we get what are known as " dry seasonal forms " 

 and " wet seasonal forms," i.e., that a larva that feeds up during the 

 wet season produces an imago different from that produced from a 

 larva of the same species that has fed up during the dry season. The 

 difference sometimes occurs in the shape of the wing, sometimes it is 

 a difference of colour, more often of ocellation. So marked are the 

 differences, that the forms have, in almost all instances, been described 

 as distinct species, but Doherty succeeded, in the early part of the 

 dry season, in the Island of Sumbawa, in breeding both Melanitis 

 leda and M. ismene, from the eggs of M. leda, the two having been 

 previously considered to be distinct species. This was done by separat- 

 ing a batch of larvae of M. leda, and rearing one part under natural 

 conditions, which produced, in due course, the dry season form, ismene, 

 the other part being reared in a box, in which a wet sponge was kept, 

 in order to retain a damp atmosphere. The imagines produced from 

 the larvae reared under the latter conditions were the wet season form, 

 M. leda. De Niceville, Marshall, and others, have also reared the one 

 form of various species from eggs laid by another. 



It has been clearly shown that temperature and moisture are two 

 important factors in bringing about changes in the appearance of 

 insects, i.e., they act in such a manner as to exert a marked influence 

 in producing variation. Our climate, of course, is not suitable for 

 the production of " dry" and ' wet " seasonal forms, as it does not 

 afford the necessary conditions. It does, however, afford the condi- 

 tions (although in a much less marked degree, than some parts of 

 Continental Europe) for the production of " spring " and " summer " 

 seasonal forms. Yet, since the action of moisture is so distinctly the 

 predominant feature in bringing about the phenomena of " dry " 

 and " wet " seasonal dimorphism, it must be conceded that moisture 

 is an effective external factor in influencing the larval life in such a 

 manner as to leave a marked impress on the resulting imago, and, in 

 a moist climate like ours, there can be no doubt whatever that 

 moisture is an effective external factor in determining variation, and 

 that its general effect may be considerable, especially in those species 



* Journal of the Asiatic Society of Bengal, vol. Iviii., pt. ii., No. 1, 1889. 



