The egg (Plate 28) may be looked for in August on the upper surface of a leaf of the sallow (_Salix caprea_). According to Buckler, it is pale olive green in colour, and cylindrical in shape; the height from base to top being about equal to the width through from side to side. It has about fourteen ribs. The caterpillar in October, just before hibernation, is dingy green roughened with numerous whitish warts from which arise short bristles, some of the latter appearing to be tinged with reddish, and those along the sides longer than those on the upper part of the body; the straight lines along the back and the oblique ones on the sides are yellowish. The head and the two horn-like projections, reminding one of the horns of a slug, are reddish-grey and covered with warts and bristles. The anal points (tails), which lie close together, are tipped with reddish. It should be mentioned here that on emerging from the egg the young caterpillar is without horns; these are not developed until the first skin is thrown off, which event happens from eight to twelve days after hatching. The full-grown caterpillar is green, merging into yellowish towards the anal points (tails); the oblique stripes on the sides are yellowish, edged with reddish. The individual depicted on the plate took up a position for change to the chrysalis on June 6. It spun a mat of silk to the under side of a sallow leaf, and the next day it was found suspended by the claspers, which were grasping the silken mat. On the fourth day the chrysalis was fully developed, and from this a male butterfly emerged on June 24, an unusually early date. The chrysalis is whitish, more or less tinged with green, but having the oblique lines on the sides whitish; the veins of the wings also show up whitish. The caterpillar was well known to entomologists in this country as far back as 1758, when, in May, four were obtained from sallow at Brentwood in Essex. It usually occurs on sallow, but an instance is recorded of it refusing to eat this plant; it would probably have starved if willow, upon which it fed up, had not been substituted. A full-grown caterpillar was on one occasion found at Raindene in Sussex on poplar, which is a well-known food of the species on the Continent. Now and then a full-grown caterpillar has been met with in October, and Buckler reared two in the autumn from the egg almost to the chrysalis stage, but they died before the change was effected.