THE PERIODICAL CICADA
this garment is not a mere bag: it is provided with special pouches for the appendages or a part of them (Fig. 125, 2). The incased antennae and the labrum project backward as three small points lying against the breast. The front legs are free to the bases of the femora, though so tightly held in their narrow sleeves that their joints have no independent motion. The middle and hind legs are also incased in long, slim sheaths, but they always adhere close to the sides of the body. Thus the cicada nymph newly-hatched much resembles a tiny fish provided only with two sets of ventral fins, but when it gets into action its motions are comparable with the clumsy flopping of a seal stranded on the beach and trying to get back into the water (3).
The infant cicada knows it is not destined to spend its life in the narrow cavern of its birth, or at least it has no desire to do so. With its head pointed toward the exit, it begins at once contortionistic bendings of the body, which slowly drive it forward. By throwing the head and thorax back, the antennal tips and the front legs are made to project so that their points may take hold on any irregularity in the path. Then a contractile wave running forward through the abdomen brings up the rear parts of the body as the front parts are again bent back, and the "flippers" grasp a new point of support. As these motions are repeated over and over again, the tiny, awkward thing painfully but surely moves forward, perhaps helped in its progress by the inclined tips of the flexible eggshells pressing against it, on the same principle that a head of barley automatically crawls up the inside of your sleeve.
Once out of the door no time is lost in discarding the encumbering garment, but it is never shed in the nest under normal conditions. If, however, the nest is cut open and the hatching nymph finds itself in a free, open space, the embryonic sheath is cast off immediately, often while the posterior end of the insect's body is still in the
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