INSECTS
cases by the splitting of an outer sheath of the egg (Fig. 92), exposing the glistening, black, true shell of the egg within. Then, from one to several days later, the shell itself shows a cleft within the rupture of the outer coat, extending along hall the length of the exposed egg surface and down around the forward end (Fig. 93 C). From this split emerges the sort head of the young aphis (D), bearing a hard, toothed crest, evidently the instrument by which the leathery shell was broken open, and for this reason known as the "egg burster." Once exposed, the head continues to swell out farther and farther as if the creature had been compressed within the egg. Soon the shoulders appear, and now the young aphis begins squirming, bending, inflating its fore parts and contracting its rear parts, until it works its body mostly out of the egg (E, F) and stands finally upright on the tip of its abdomen which is still held in the cleft of the shell (G).
The young aphis at this stage, however, like the young roach, is still inclosed in a thin, tight-fitting, membranous bag having no pouches for the legs or other members, which are all cramped within it. The closely swathed head swells and contracts, especially the facial part, and suddenly the top of the bag splits close to the right side of the egg burster (Fig. 93 H). The cleft pulls down over the head, enlarges to a circle, slides along over the shoulders, and then slips down the body. As the tightly stretched membrane rapidly contracts, the appendages are freed and swing out from the body (I). The shrunken pellicle is reduced at last to a small goblet supporting the aphid upright on its stalk, still held by the tip of the abdomen and the hind feet (I). To liberate itself entirely the insect must make a few more exertions (J), when, finally, it pulls its legs and body from the grip of the drying skin, and is at last a free young aphid (L).
The emergence from the egg and from the hatching membrane is a critical period in the life of an aphid. The
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