The family of Pieridæ, or whites, again afford us admirable examples of the development of spots. The prevailing colours are white, black and yellow: green appears to occur in the Orange-tips (Anthocaris), but it is only the optical effect of a mixture of yellow and grey or black scales. The species are very variable, as a rule, and hence of importance to us; and there are many intermediate species on the continent and elsewhere which render the group a most interesting study.

The wood white (Leucophasia sinapis) [Fig. 1, Plate IV.], is a pure white species with an almost square dusky tip to the fore-wings of the male. In the female this tip is very indistinct or wanting, [Fig. 4, Plate IV.] In the variety Diniensis, [Fig. 2, Plate IV.], this square tip appears as a round spot.

The Orange-tips, of which we have only one species in Britain (Anthocaris cardamines) belongs to a closely allied genus, as does also the continental genus Zegris. The male Orange-tip (A. cardamines) is white with a dark grey or black tip, and a black discoidal spot. A patch of brilliant orange extends from the dark tip to just beyond the discoidal spots. In the female this is wanting, but the dark tip and spot are larger than in the male.

Let us first study the dark tip. In L. sinapis we have seen that it extends right to the margin of the wing in the male, but in the female is reduced to a dusky spot away from the margin. In A. cardamines the margin is not coloured quite up to the edge, but a row of tiny white spots, like a fringe of seed pearls, occupies the inter-spaces of the veins. On the underside these white spots are prolonged into short bars, see [Plate IV]. In the continental species A. belemia we see the dark tip to be in a very elementary condition, being little more than an irregular band formed of united spots, there being as much white as black in the tip, [Fig. 5, Plate IV.] In A. belia, [Fig. 6, Plate IV.], the black tip is more developed, and in the variety simplonia still more so, [Fig. 7, Plate IV.] We here see pretty clearly that this dark tip has been developed by the confluence of irregular spots.

Turning now to the discoidal spot we shall observe a similar development. Thus in:—

A. cardamines, male,it is small and perfect.
Do. female,"larger"
A. belemia"large"
A. belia"large with white centre.
Do. v. simplonia"small and perfect.
[15]A. eupheno, female,"nearly perfect.
Do. male,"a band.

We here find two distinct types of variation. In A. belia we have a tendency to form an ocellus, and in A. eupheno the spot of the female is expanded into a band in the male.

The orange flush again offers us a similar case; and with regard to this colour we may remark that it seems to be itself a development from the white ground-colour of the family in the direction of the red end of the spectrum. Thus in the Black-veined white (Aporia cratægi) we have both the upper and under surfaces of the typical cream-white, for there is no pure white in the family. In the true whites the under surface of the hind-wings is lemon-yellow, in the female of A. eupheno the ground of the upper surface is faint lemon-yellow, and in the male this colour is well-developed. The rich orange, confined to a spot in G. rhamni becomes a flush in G. Cleopatra, and a vivid tip in A. cardamines. These changes are all developments from the cream white, and may be imitated accurately by adding more and more red to the primitive yellow, as the artist actually did in drawing the plate.

In A. cardamines the orange flush has overflowed the discoidal spot, as it were, in the male, and is absent in the female. But in A. eupheno we have an intermediate state, for as the figures show, in the female, [Fig. 8], the orange tip only extends half-way to the discoidal spot, and in the male it reaches it. Moreover it is to be noticed that the flow of colour, to continue the simile, is unchecked by the spot in cardamines, but where the spot has expanded to a bar in eupheno it has dammed the colour up and ponded it between bar and tip. An exactly intermediate case between these two species is seen in A. euphemoides, [Fig. 10, Plate IV.], in which the spot is elongated, and dribbles off into an irregular band, into which the orange has trickled, as water trickles through imperfect fascines. This series of illustrations might be repeated in almost any group of butterflies, but sufficient has been said to show how spots can spread into patches, either by the spreading of one or by the coalescence of several.