Page:Hardwicke's Science-Gossip - Volume 1.pdf/47

] for she folds her wings together on his approach, and then the flirtations, pursuits, refusals, and pretended departures commence again.

These performances sometimes last for more than half an hour, no inconsiderable portion of a butterfly's lifetime. When they have ended, the female deposits its eggs, several hundred in number, upon some portion of a cabbage-leaf. The eggs are like little pyramids, three or four times as high as wide, and grooved by deep channels, which separate the rounded, undulating sides from each other. The Pieris arranges its eggs in a most artistic manner, side by side, and, having glued them firmly to the leaf, leaves them entirely to their fate. By far the greater number of them perish, but still some are hatched, and thus insure the perpetuation of the species.

Every one knows that there springs from each of these eggs a worm-like animal called a caterpillar, which must pass into the intermediate condition of chrysalis before it will become a perfect butterfly.

The egg which our Pieris lays is much smaller than a millet-seed, and the caterpillar which emerges from it is proportionally diminutive. When fully formed, however, it measures one inch and a half in length, and about 1-5th of an inch in width, and 1-6in in depth. We see what a great difference there is in size between the animal when it emerges from the egg, and when it is fully formed, and how rapidly the increase takes place. Moreover, this growth is not gradual, as in most other animals. We may describe it as occurring suddenly, and by a series of formative leaps taken at each of those periods ordinarily called moultings. In fact, as soon as it leaves the egg the young caterpillar eats with a voracity too familiar to our gardeners, but, nevertheless, does not increase in size.

After some days this enormous appetite is lost; the caterpillar becomes quite languid, and its skin loses its colour and appears to wither. It then crawls away to some sheltered locality. If we follow it to its retreat, we shall see it attach itself firmly to the ground, alternately contracting and inflating its body and twisting it about in every way; then resting for a while, as if completely exhausted, and finally commencing anew. Sometimes whole hours are spent before we can see the object of all these tiresome operations. Eventually the skin bursts at the third or fourth ring, and splits in a straight line from one end of the body to the other. The caterpillar now pushes out first its head and afterwards its entire body, and appears in a new skin as flexible and as brilliantly-coloured as ever. It has also increased in size, so that it would be quite impossible to enclose it in the case which before enveloped it. Its organs have increased in volume, but having been pent up and compressed by the old skin, when suddenly liberated they attained their proper size, as it were, through their natural elasticity.

There are several moultings gone through before the caterpillar arrives at its adult size and acquires its final characters. At this period we can distinguish but two anatomical regions in our insect—the head and the trunk. The head is small, of a blue colour picked with black, covered with a hard skin, and provided with six simple eyes, which are quite separate from each other. The mouth, as in other caterpillars, is formed for dividing and chewing the tough leaves of cabbage and other cruciferous plants. It is provided laterally with a pair of less powerful jaws, which are partly concealed by an upper lip and a wide lower one. In the middle of the latter may be seen a small tubular elongated organ, pierced by a microscopic aperture; this is the spinning apparatus, by which is made the soft wool-like material which the animal will soon require.

The body of the caterpillar is of cylindrical form, and is composed of twelve almost similar rings. It is of a greenish or yellowish grey colour, marked by three yellow bands which pass from end to end, and is covered with black spots. These spots are little tubercles, each of which carries a white hair, easily seen with a pocket lens. There are eight pairs of feet for the purpose of locomotion, and, as in all caterpillars, these are of two kinds. The three first of each side are conical, jointed, and terminated by hooklets or little claws; these are the horny or true feet. The others are termed membranous or false feet. The latter are like large tubercles, whose ends are truncated and furnished with a circle of hooklets. The most remarkable feature in connection with these is, that the caterpillar can move them in every direction, can push them out, or draw them into the body so completely that there is hardly a trace left of the positions they occupied. There is on each side of its body and extending over ten segments, a series of little orifices, each of which is surrounded by a brown circle; these are the stigmata, or apertures through which the air is admitted to the respiratory organs.

The caterpillar of the cabbage butterfly