CXXIV 



Heterocera, being sporadically found among Geometridae, 

 Arctiidae, Lymantriidae, Lasiocampidae, Hepialidae, and 

 obtaining in all species of Psychidae, Heterogynidae and 

 Somabrachidae ; in Noctuids this line of development is fairly 

 advanced in certain Alpine species, tbe females of which seek 

 safety in crawling into the ground or the herbage like a Carabid 

 beetle rather than trusting to the shortened wings, while in 

 some other Noctuids the wings are quite reduced. As a rule 

 the females of Heterocera are larger than the males, the 

 difference frequently being so great that one would hardly 

 believe in the specimens being the sexes of the same species, as 

 for instance in some Lasiocampidae and Saturniidae. On the 

 other hand, it happens also that the male is rather larger than 

 the female and, moreover, has acquired a modified contour 

 of the wings, as for instance in some species of the Saturnian 

 genus Oxytenis, of which the males have been placed in one 

 genus and the females in another far removed from the former. 

 The differences in the colouring and pattern of the sexes are 

 likewise often very striking in Heterocera. All this shows that 

 the Heterocera have the faculty of acquiring a great sexual 

 diversity. That being so, is it not remarkable that there is 

 among night-flying moths no such clear-cut polymorphism as we 

 so frequently observe among butterflies ? I said night-flying 

 moths, because there is sharply marked polymorphism also 

 among Heterocera, for instance among Arctiidae, Agaristidae, 

 and Zygaenidae, but — and this is an important point — the 

 species in which this obtains are day-fliers like the butterflies. I 

 mention as an illustration the Agaristid Immetalia saturata, a 

 day-flying moth to which I shall refer again later on. Here 

 sunshine and polymorphism are coincident, and does it not 

 look as if sunshine was a condition for the development of 

 polymorphism ? But that is not- all. In the majority of 

 polymorphic day-fliers and in numerous sexually dimorphic 

 species the pattern and colour are more or less the same as 

 those of other species occurring along with them. The 

 various forms of Papilio lysithous, from S. E. Brazil, fly in the 

 same localities as the various distinct species of Aristolochia 

 Papilios which they resemble. The numerous forms of 

 Pseiiddcraea eurytus are repetitions of the colouring and jDattern 



