In order to make its manoeuvres and the difficulty of them the more easily comprehended, let us (to follow Messrs. Kirby and Spence in the same matter) put a case of a somewhat similar kind before the readers by way of supposition. Country fellows at wakes and fairs frequently--for the diversion of the company there assembled, or for a prize of some value in their estimation, perhaps a fat pig, or a leg of mutton--run races in sacks which are tied close about their necks, and of course tumble about a good deal, and display anything but a graceful mode of progression. "Now," say these authors, "take one of the most active and adroit of these, bind him hand and foot, suspend him by the bottom of his sack, with his head downwards, to the branch of a lofty tree; make an opening in one side of the sack, and set him to extricate himself from it, to detach it from its hold, and suspend himself by his feet in its place. Though endowed with the suppleness of an Indian juggler, and promised his sack full of gold for a reward, you would set him an absolute impossibility; yet this is what our caterpillars, instructed by a Beneficent Creator, easily perform!" [Illustration: _This Cut shows the entire change from the first rupture of the skin to the casting away of the old skin._] [Illustration: _Tail of a Pupa magnified to show the toothed parts._] Let us proceed to show in what manner the caterpillar performs this wondrous feat. After suspending itself in the way already described, a little time generally elapses, during which the insect by turns contracts itself, and then dilates again. At length its skin splits near its head, and a portion of the pupa appears, which acts like a wedge, and, being thrust partly through the slit, causes it to tear still higher and higher towards the tail. The insect continues its painful labours, swelling and contracting alternately, so as to push the torn skin higher and higher up, as one would roll off a stocking, until at length the old skin is folded into several rolls, and is quite at the tail. But the task is as yet only half accomplished; the most arduous and difficult part remains to be done. The pupa is shorter than the larva, and consequently hangs out of reach of the silken button in which the latter was firmly fixed by its hind legs. It seems now as if the poor insect must fall, for there appears no way for it to get up to the silk anchorage, and the folds of the pushed-up old skin are all that retain it in its position, which, as may be imagined, is far from a secure kind of fastening. How is it to disengage itself from its case, and be suspended in the air while it climbs up to take its place? Without arms or legs to support itself, the anxious spectator expects to see it fall to the earth. His fears, however, are groundless; the supple segments of the pupa's abdomen serve in the place of arms. Between two of these, as with a pair of pincers, it seizes on a portion