Page:The Butterflies of India, Burmah and Ceylon Vol 1.djvu/26

2 difficulty in discriminating and identifying insects, though, at the same time, the scientific value of the study would be largely reduced; but it is not so. First we find that in some species the sexes are differentiated—the females differing from the males either in colour or style of markings, and even in form and outline of the wings, these differences being constant in each sex. Again, we find that in different climates Butterflies, apparently the same in general character, present constant differences in colour or style of marking of more or less importance, but frequently sufficient to justify the description of each form under a separate name. Again, in different localities, even where the differences of climate are inappreciable, such as notably the various islands of an archipelago, and in a lesser degree disconnected valleys of a mountain range, the Butterflies of each locality often present constant and well marked differences, particularly in the size and extent of markings, thus forming what have been termed geographical" varieties in contradistinction to "climatic" varieties; and yet, again, we have the most interesting and important variation of all occurring among Butterflies which have two or more broods in the year; and in which the summer and autumn broods differ from the spring brood more or less, sometimes so widely in colour and markings that, until the question was conclusively set at rest by breeding Butterflies of the one type from the eggs of Butterflies of the other, the two forms were described and universally accepted as representing two distinct species.

Thus we have "sexual," "climatic," "geographic," and "seasonal" variations, each of which can be referred more or less confidently to known external causes; but, in addition to these, the study of the subject is complicated by individual variations, which appear to be quite irrespective of external conditions; such variations are exhibited in different species in different degrees, or possibly the tendency to vary may pass through more or less active or dormant stages at different epochs of the history of each group. At the present time some species, notably among the Junonias, are wonderfully constant to the type; others, again, differ so universally among themselves that scarcely any two specimens, even from the same locality, are alike. Of such variations the under-surfaces of the wings in Melanitis leda and M. ismene, and in the great "oak-leaf" Butterflies of the genus Kallima, are noteworthy instances; also the numbers and size of the ocelli in many genera of the Satyrina : and, again, instead of a single typical form, with minor differences in each individual, we sometimes find, as in the case of Papilio polytes or P. memnon, that there are several distinct types, described by the earlier authors as distinct species, t)ut which in reality spring promiscuously from the same stock—a single batch of the eggs laid by a single female having been found to produce two or more of the different forms. And, lastly, we find that specimens aberrant from the type occur singly and casually here and there from time to time, and coexisting in the same localities with specimens of the normal form. It may easily be conceived that among insects with such manifold tendencies to variation and such brief periods of existence, the clue to the laws which govern such developments may most readily be found.

The phenomenon of "mimicry," too, is deserving of the closest scientific observation. One of the earliest puzzles met with by the observer of Butterflies lies in finding males and females in company, apparently belonging not only to different species, but different genera, and even families; but closer examination reveals that the female in reality belongs to the same species as the male, although its coloration and markings are excellent imitations of a totally different Butterfly, generally of a much commoner Butterfly, and almost always of a Butterfly less subject than its own species to destruction by birds and reptiles. The subject is too extensive to enter on here, but it is one that should never be lost sight of in investigating the life-history of insects.

The field for observation offered by the British Indian Empire is as varied as it is vast. We have every climate, from the eternal snows to the tropics— and all the most interesting