SEASONAL DIMORPHISM OF LEPIDOPTERA. 249 



which is either entirely absent in prorsa, or at least is slightly 

 indicated on the hind wings only ; on the other hand, lyrorsa 

 exhibits the white band below, which is covered with yellowish 

 and brownish tones in levana. V. levana, therefore, at any rate 

 while at rest, is well adapted to the numerous dry leaves of the 

 spring wood ; I do not know, however, whether they rest on the 

 ground. V. prorsa, indeed, spends the night on plants— brambles, 

 danewort (Samhucus ehulus), and the like — and is well protected 

 by this very white band, which is also visible when it is at rest, 

 in the neighbourhood of white flowers. 



Although the upper side of most butterflies has no sympathetic 

 colouring, still I will in no way dispute that such may occur in 

 quite a general sense, and even the levana-iovm may to some 

 extent be protected in flight by its agreement in colour with the 

 yellowish-brown dry leaves of the spring wood. But generally 

 protective colouring of the upper side will arise as mimicry. 



Although I have considered prorsa under this point of view, 

 I should still expect that cases of mimicry would be rarely con- 

 nected with seasonal dimorphism. It is not, indeed, impossible, 

 but improbable, that any tropical species has mimicked one of the 

 protected species for the rainy season, and another protected 

 form for the dry season. It is the case that a species requiring 

 protection has adapted itself to a different protected Danaid 

 in Ceylon than in Malacca and in Java ; examples are also 

 known where the male resembles a different protected type 

 from the female, but hitherto, at least, it has not been observed 

 that periodic dimorphism occurs in a species with double 

 mimicry. 



It is still more difficult to decide whether we have to do with 

 pure direct seasonal dimorphism in any particular case. The 

 experiments justify its assumption with Chrysophanus pliloeas ; 

 and with Pararge egeria and Vanessa urtlccB the climatic varia- 

 tions may well be regarded as the direct effects of the different 

 temperatures ; but it is difficult to decide whether, and, if so, 

 how far, double adaptation takes part in this or — with climatic 

 variations — sexual selection. When, for example, Merrifield* 

 finds with a Geometer, Selenia illustraria, that low temperature 

 applied to the pupae impresses the perfect insect with the dark 

 winter form, and high temperature the bright summer form, this 

 might be well regarded as the direct effect of temperature. But 

 when one considers that the actual cause of the variability of 

 both broods might possibly be an adaptation of the upper side of 

 the moth to the different surfaces, on which it sits in the spring 

 and in the summer, the possibility remains that processes of 

 selection and not temperature have produced them. 



* Merrifield, *' Systematic Temperature Experiments on some Lepi- 

 doptera in all their Stages," in Trans. Ent. See. Lond. 1890, p. 131. 



