Butterflies (Rhopalocera) are grouped into four sub-families, as under:—
1. Nymphalidæ, having the fore-legs rudimentary, and the pupæ suspended from the base of the abdomen.
2. Erycinidæ, in which the males only have rudimentary fore-legs.
3. Lycænidæ, in which the fore-legs of the males are smaller than those of the females, and terminate in a simple hook.
4. Papilionidæ, which have six perfect pairs of legs, and in which the pupæ assume an upright posture, with a cincture round the middle.
It may, at first sight, appear curious that the imperfect-legged Nymphalidæ should be placed at the head of the list, but this is based upon sound reasoning. The larva consists of thirteen segments, and, in passing to the mature stage, the second segment alone diminishes in size, and it is to this segment that the first pair of legs is attached. Looking now to the aerial habits of butterflies, we can understand how, in the process of evolution towards perfect aerial structure, the legs, used only for walking, would first become modified; and, naturally, those attached to the segment which decreases with development would be the first affected. When this is found to be combined with an almost aerial position of the pupæ, we see at once how such insects approach nearest to an ideal flying insect. It is a general law that suppression of parts takes place as organisms become specialized. Thus, in the mammalia, the greatest number of toes and teeth are found in the lowest forms and in the oldest, simplest fossil species.
A butterfly is, indeed, little more than a beautiful flying machine; for the expanse of wing, compared with the size of the body, is enormous.
[CHAPTER XI.]
The Colouration of Insects.
(Continued.)
General Scheme of Colouring. So various are the patterns displayed upon the wings of butterflies, that amidst the lines, stripes, bars, dots, spots, ocelli, scalloppings, etc., it seems at first hopeless to detect any general underlying principle of decoration; and this is the opinion that has been, and is still, held by many who have made these insects a special study. Nevertheless, we will try to show that beneath this almost confused complexity lie certain broad principles, or laws, and that these are expressed by the statement that decoration is primarily dependent upon structure, dependent upon the laws of emphasis and repetition, and modified by the necessity for protection or distinction.
To render this subject as plain as possible, British species will be selected, as far as possible, and foreign ones only used when native forms do not suffice.