Variation consists chiefly of increase or decrease in the size of the black markings. At least one specimen is known in which all the wings are uniform smoky black. This is in the collection of Mr. A.B. Farn, and was captured near Rochester, Kent, in 1871. Between this extreme and specimens with the black markings of typical proportions there are various modifications; but striking aberrations are rare in this country. Sometimes there is entire or partial absence of black pigment. A remarkable example of this kind of aberration, taken on the cliffs between Dover and Walmer some years ago, is described as of a clear milky-white colour, and has not, either on the upper or under side of the wings, the smallest speck of black. The ground colour is sometimes decidedly yellow, and very occasionally brownish. The life-history of this butterfly is figured on Plate 74. The egg is whitish, opaque, with a dark speck on the apex; base flattened and slightly hollowed; finely reticulated, but without distinct striations or anything resembling ribs. The eggs are laid in July, and are not attached to anything. The caterpillar when full grown, is whity-brown in colour with brownish lines. The head is brown, tinged with pink, and the tail-like points on the last ring are pink. The head, as well as the body, is clothed with short hair. The chrysalis is also whity-brown with a pinkish tinge, browner speckling on the wing cases, and the body is marked down the back with yellow. Hellins says, "It hibernates when very small, becomes full fed in June, and changes to a pupa without suspending itself in any way, or making a cocoon; I think it would hide itself, as my examples did; I found they had got among the thick moss with which I had furnished the bottom of their cage, and apparently made little hollows for themselves by turning round." Cock's-foot grass (_Dactylis glomerata_) and cat's-tail grass (_Phleum pratense_) are given as food-plants, but the caterpillars in confinement seem to eat any kind of grass that is supplied. The butterfly is found in most of the Midland counties and in nearly all of the Southern ones, but is especially common on the chalk downs of the South-west. It does not occur in Ireland or Scotland, and seems to be absent from the Northern counties of England except Yorkshire. In the last-named county it was supposed to be extinct, but during the past ten years it has been observed at Sledmere, and near Scarborough and Helmsley. It is also reported to be not uncommon in three localities not far from York. [Illustration: _Pl._ 72. =Milkweed Butterfly.= _Egg, natural size and enlarged; caterpillar and chrysalis (after Smith)._] [Illustration: _Pl._ 73. =Marsh Fritillary.= 1, 3, 5, 9, 10 _male_; 2, 4, 6, 7, 11 _female_. 1, 2, 4, 6, 7, 9 _English_; 8 _Welsh_; 3, 5, 10, 11 _Irish_.]