This usually scarce butterfly (Plate 21) is of a primrose-yellow colour in the male, and, as a rule, almost white in the female; sometimes the latter sex is of the yellow male colour. The outer margin of the fore wings is broadly black in both sexes, but there are some more or less united spots of the ground colour in the black towards the tips of the wings, and below vein 3 the black is usually confined to the outer margin. There is a black spot near the middle of the wing, and some blackish dusting quite near the base of the wing. The hind wings have a pale orange central spot, sometimes two spots, and the blackish border on the outer margin is generally narrow, and often interrupted or broken up into spots. The fringes of all the wings are pinkish, as also are the antennæ. The egg is pearly yellowish-white when first laid; a few days later the top becomes transparent, white, and glassy, shading downwards into yellow, and then clear rosy orange; the base is pale, but less transparent than the top. It has a number of transverse ribs, ranging from nineteen to twenty-two. Before the caterpillar hatches out, the egg changes to a purplish leaden colour. [Illustration: _Pl._ 18. =Wood White Butterfly.= _Eggs, natural size and enlarged; caterpillar (after Buckler) and chrysalis._] [Illustration: _Pl._ 19. =Wood White Butterfly.= 1, 4, 6 _male_; 3 _do. (var.)_; 2, 5, 7 _female_.] The caterpillar in October, before hibernation, is about a quarter of an inch long, and deep clover-green in colour; it has a number of pale, shining warts along the back, from each of which there is a moderately long black bristle, and there is a pale yellowish-white stripe above the black spiracles. The head is pale ochreous green, with warts and bristles as on the body. It rests upon a pad of silk spun on the centre of a leaflet. When full grown the colour is clear light green, but has a darkish velvety appearance, due to the entire surface being densely sprinkled with black warts, the bristles from the warts on the back are black, and those on the lower surface are white, the line above the spiracles, which are white outlined with black, is made up of lemon-yellow, orange-vermilion, and orange with an upper border of white. The head, claspers, and legs are green. It feeds in June, and again in August, on clover, trefoil, etc. The figure on Plate 20 is after Hübner. The chrysalis is very similar to that of the Clouded Yellow, the chief differences are that the head-beak of the present species is straight instead of being slightly upturned, and the tip of the wing-case extends further down the body. The above particulars of the early stages of the Pale Clouded Yellow are adapted from Mr. Frohawk's account of the life-history of the species (_Entomologist_, 1892 and 1893).