PROCESS OF THE CHANGE. 219 



impossibility ; yet this is what our caterpillars, in- 

 structed by a Beneficent Creator, easily perform !" 

 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 conse- 

 quently 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, 



