The Insect World: Being a Popular Account of the Orders of Insects

Fig. 124. Fig. 125. Fig. 126.

A conical pupa. Pupa having angular projections. Angular pupa of a Butterfly.

sides, little humps, eminences broader than they are thick, ending in a sharp point (Fig. 125). The head of the angular pupae terminates sometimes in two angular parts, which diverge from each other like two horns (Fig. 126). In some other cases they are curved into the form of a crescent. These appendages sometimes give to the pupa the appearance of a mask, especially as an eminence placed on the middle of the back is rather like a nose, and the small cavities may represent the eyes (Fig. 125). The colours of angular pupae attract our attention. Some are superbly tinted; they appear to be wrapped in silk and gold. Others have only spots of gold and silver on their belly or their back. All, however, have not this remarkable splendour, not these metallic spots. Some are green, yellow, and spotted with gold. Generally they are brown. Re'aumur has shown that this golden colour is not due, as was thought for a long while, to colouring matter, but to a little whitish membrane, placed under the skin, which reflects the light through the thin outer pellicle, in such a manner as to produce the

loo THE INSECT WORLD.

optical illusion which imparts to the robe of the chrysalis the golden hues of a princess in grand costume. Ail is not goid that giittersy Reaumur proves literally, in the case of chrysalis.*

Let us add that the chrysalis remains thus superbly dressed as long as it is tenanted, but loses its colour as soon as the butterfly has quitted it. The cone-shaped pupae belong to the twilight and night-flying Lepidoptera, and to those butterflies whose caterpillars are onisciform, or in shape resembling a wood-louse. They are generally oval, rounded at the head, and more or less conical at the lower end. Their colour is generally of a uniform chestnut brown.

What a mystery is that which is accomplished in the transition from the chrysalis to the perfect state! Those great changes from the larva state to that of the pupa, and from the pupa to that of the imago, are accomplished with such rapidity, that the phenomena were looked on as sudden metamorphoses, like those related in mythology. It has been thought also that there was in these changes from one state to another a sort of resurrection. There is here neither sudden metamorphosis, nor, as we will show, resurrection. In fact, the chrysalis is a living being; it indeed shows its vitality by exterior movements. Under the old skin of a caterpillar about to moult, under the envelope which is soon to be cast oif, the new integuments are being prepared.

Some days before the moult, split the caterpillar's skin, and you will find the skin which is to take its place already beneath. If, some days before the transformation of the caterpillar into a chrysalis, it is dissected, the rudiments of wings and antennae may be discovered. If a chrysalis is examined on the outside, all the parts of the future insect can be distinguished under the skin: the wings, the legs, the antennae, the proboscis, &c.; only, these parts are folded and packed away in such a manner that the chrysalis can make no use of them. It could not, moreover, make use of them on account of their incomplete development. Fig. 127 shows, after Reaumur,t; a chrysalis magnified and seen from its lower side, on which we observe:— a, the wings; l?b, the antennae; /, the trunk or proboscis.

There is a moment when these parts, pressed one against each other, and as it were swathed up like a mummy, are very easily seen, for they are, as we may say, laid bare. This moment is that in

• The word is derived from XP^^^^^ go^^ 5 fo"^ ^li^t reason pupa is a better word than chrysalis, as this only strictly applies to a very small number; for the same reason aurelia is a bad word. — Ed. f Tome i., p.. 382, planche 26, Fig. 6.

i6i LEPIDOPTERA.

which the pupa has just quitted the caterpillar's skin. It is then still soft and tender. Its body is moistened with a liquid, which, drying rapidly, becomes opaque, coloured, and of a membranous consistency. The result is that the parts which did not cohere in the least when the chrysalis made its first appearance, are fastened together, so that although they could at first be seen, through a layer of transparent fluid, they are now hidden under a sort of veil or cloak. It is necessary, then, to seize the moment of the birth of the chrysalis, to observe it accurately.

On examining the pupa before the liquid which pervades these parts has had time to dry, it resembles the perfect insect. All the exterior parts which belong to the imago can be distinguished. One recognises the head, which is then resting on the thorax; the two eyes and the antennae (Fig. 128), which are brought forward like two ribbons; the wings also brought over the thorax, but these are separated artificially in the drawing we have given after

Reaumur;''^ and lastly in the space left between the wings, the six legs, and the body of the insect. To sum up: the pupa, when it approaches Fig. 127. the period for being hatched is only a swaddled Chrysalis of the large butterfly. Directly it has strength enough to rid Tortoise-shell Butterfly itself of its wrapping, the insect frees itself from magnified,( Vanessalowerpolychloros),seenside.from theits fetters; it flies away, brilliant and free, and its many-coloured wings glitter in the sun.

The duration of the pupa state is variable, according to the species and the temperature. Re'aumur placed in a hot-house, in the month of January, some pupae which, in the ordinary course of things, would not have been hatched till the month of May, and a fortnight afterwards the imago had appeared in each case. On the other hand, he shut up some pupae in an icehouse during the whole of a summer, and thus retarded their being hatched by a whole year. The influence of the temperature on the period of emerging, and, consequently, the influence of the seasons on the length of this

period, are completely brought to light *by these experiments.! * Tome i., p. 382, planche 26, Fig. 7. t They hardly seem from later experiments to be so fully explained. It is a 63

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We will now see how the insect delivers itself from the last skir». To quit the pupa case is not so laborious an operation as it was for the same insect to quit the caterpillar's skin. This is because the pupa case is drier; it does not adhere to every part of the body, and is brittle. Those insects which are enclosed in a cocoon free themselves of the pupa envelope in the cocoon itself. To witness the last operation, the cocoon may be opened, and the pupa drawn out

Fig. 128.— Chrysalis of the Large Tortoise-shell Butterfly [Vanessa polychlo whose different parts have been opened before they were fastened down. {a, wings; bo, antennae; /, trunk, or proboscis.)

of it with care. If it is then placed in a box, the metamorphosis may be observed. To study this last evolution more at his ease, Reaumur covered a large extent of the wall of his study with pupas of the Vanessa polychloros and other species.

When the parts of the body of the insect have attained a certain degree of solidity within the envelope, it has no great difficulty in making the thin and friable membrane which surrounds it split in diiferent places. If it even distends itself or moves, a small opening will be made in the dried skin. If the movements persist, the

s^rell-known fact that many insects remain in this state a variable time— the Small Eggar {Bombyx lanestris) sometimes as many as seven years, — Ed.

LEPIDOPTERA.

opening increases in size, and very soon allows the imago to emerge. It is on the middle of the upper part of the thorax that the envelope begins to split. The split extends over the middle of the forehead and back. The pieces of the thorax open, separate themselves from the other parts to which they were fixed, and the insect can take advantage of the opening which is made, and escape. Little by little also it advances its head. The head is the first out of the old skin, and the insect sets itself entirely free.

This occupies rather a long time; for we must remember that, under the pupal envelope, its legs, its antennge, its wings, and many other parts, are enclosed in special cases. These peculiar circumstances show that the animal has much trouble and must employ some time in setting free all the parts.

At last our prisoner has come out of its narrow cell, and is delivered from its old covering. What Moth just ernerged. poet can describe to us the sensations of this charming and frail creature which has just risen from the tomb, and for the first time is enjoying the splendid light of day, the radiant sky, and the flowers redolent with delicious perfumes, which are inviting it to kiss and caress them!

The wings strike one most. They are very small at the time of birth.

Fig. 129 represents, after Re'aumur,'^ a moth at the moment in which it has just emerged from the pupa. But at the end of a short period the wings become developed; only they are wrinkled, as Fig. 130, given by Reaumur, represents. Y'vg. 130.

Re'aumur having taken between his fingers a Moth foldedwhose up.wings are very short wing of a butterfly which was just hatched, drew it about gently in all directions. He succeeded thus in giving it the whole extent it would have assumed naturally. According to Reaumur the wing of a butterfly just born, which appears so small, is really already provided with all its parts, only it is folded and re-folded on itself. He supposes that what his hands did to lengthen the butterfly's wings, is done naturally

• Tome i., p. 654, plaiiche 46, Fig. i.

by the liquids which are contained in the insect which has just emerged, and whose wings are no longer confined in their cases. At the time of its birth the wings are flat and thick; as they grow, little by little they spread themselves out and become curled up. When they are completely developed and flattened the wings become firm and hard imperceptibly, and this firmness extends at the same time to the whole of the body. Figs. 131 and 132, borrowed, like the preceding, from the 14th