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.

The body of by far the greater number of species is either darker or of the same tint as the mass of the wings; and only in rare cases lighter. When the body has different tints, it is generally found that the thorax and abdomen differ in colour, and in many cases the base of the thorax is emphasized by a dark or light band.

On the wings the functional importance of the parts attached to the body is generally darker, perhaps never lighter, than the ground of the wing, and is frequently further emphasized by silky hairs. This has already been sufficiently pointed out.

The wing area may be divided into the strong costal margin, the hind margin, the nervules, and the spaces; and, however complex the pattern may be, it is always based upon these structure lines.

In the majority of insects the costal margin is marked with strong colour. This may be noticed in _Papilio Machaon_, _P. merope_, _Vanessa antiopa_, and the whites in Plate IV. The extreme tip of the fore-wings is nearly always marked with colour, though this may run into the border pattern. This colour is dark or vividly bright, and we know no butterfly, not even dark ones, that has a light tip to the wings. Sometimes, it is true, the light bead-border spots run to the tip, but these are not cases in point. The development of tips has been traced in