aterpillar_ 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 Rapae_).

The smaller butterfly with more dusky markings, formerly known as _P.
Metra_, has been recently proved to be merely a variety of _Rapae_, a Mr.
J. F. Dawson having reared a brood of caterpillars all _exactly similar_ in
appearance, which eventually produced every variety of _P. Rapae_ 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