Outwardly resembling the last in almost every respect but that of its inferior size, this species shares the gardener's malediction with its larger, but perhaps less destructive, relative; for the caterpillar of _Rapæ_, though smaller, bores into the very heart of the cabbage, instead of being content with the less valuable outer leaves, as _Brassicæ_ is. From this pernicious habit the French call this grub the _ver du coeur_. The colour of this _caterpillar_ is pale green, with a yellow line along the back, and a dotted one of the same colour on each side. The _chrysalis_ is nearly like that of the last in shape, but of course smaller, and is of a more uniform brownish or yellowish tint. [Illustration: X.] {85} This butterfly occasionally multiplies immensely, and is given to migrating in vast armies to distant settlements, sometimes crossing the sea to effect this purpose. Here is an extract from a Kentish newspaper, describing an occurrence of this phenomenon:-- "One of the largest flights of butterflies ever seen in this country, crossed the Channel from France to England on Sunday last. Such was the density and extent of the cloud formed by the living mass, that it completely obscured the sun from the people on board our Continental steamers, on their passage, for many hundreds of yards, while the insects strewed the decks in all directions. The flight reached England about twelve o'clock at noon, and dispersed themselves inland and along shore, darkening the air as they went. During the sea-passage of the butterflies, the weather was calm and sunny, with scarce a puff of wind stirring; but an hour or so after they reached _terra firma_, it came on to blow great guns from the S. W., the direction whence the insects came." A contemporary account states that these were the small white butterflies (_Pieris Rapæ_). The smaller butterfly with more dusky markings, formerly known as _P. Metra_, has been recently proved to be merely a variety of _Rapæ_, a Mr. J. F. Dawson having reared a brood of caterpillars all _exactly similar_ in appearance, which eventually produced every variety of _P. Rapæ_ and _P. Metra_. Mr. Curtis, in his "Farm Insects," mentions the capture, near Oldham in Lancashire, of a male specimen, which had all the wings of a _bright yellow_ colour. Most juvenile butterfly hunters, unblest by scientific knowledge of insect life, imagine that this and the last owe their difference in size simply to their being old and young individuals of the same name; forgetting--or, rather, never having heard--that butterflies never grow in the slightest degree after once getting their winged form; only as caterpillars do they grow. {86} The male is distinguished from the female by having only _one round black spot_, or sometimes none, on each _upper_ wing, whilst the female is spotted as in the engraving. The under side of the hind wings is dull yellow, lightly powdered with black scales.