242 



MOTIONS OF INSECTS. 



effect their escape from their various prisons and become den- 

 izens of the air, especially as you are aware that each is 

 shrouded in a winding-sheet and cased in a coffin. In most, 

 however, if you examine this coffin closely, you will see re- 

 surgam written upon it. What I mean is this. The pu- 

 parium, or case of the animal, is furnished with certain acute 

 points (adminicula), generally single, but in some instances 

 forked, looking towards the anus, and usually placed upon 

 transverse ridges on the back of the abdomen, but sometimes 

 arming the sides or the margins of the segments. By this 

 simple contrivance, aided by new-born vigour, when the time 

 for its great change is arrived, the included prisoner of hope, 

 if under ground, pushes itself gradually upwards, till reaching 

 the surface its head and trunk emerge, when an opening in 

 the latter being effected by its efforts, it escapes from its con- 

 finement, and once more tastes the sweets of liberty and the 

 joys of life. Those that are inclosed in trees and spin a co- 

 coon, are furnished with points on the head, with which they 

 make an opening in the cocoon. The pupa of the great goat- 

 moth (Cossus ligniperda) thus, by divers movements, keeps 

 disengaging itself from this envelope, till it arrives at a hole 

 in the tree which it had made when a caterpillar ; when its 

 anterior part having emerged, it stops short, and so escapes a 

 fall that might destroy it. After some repose, in consequence 

 of very violent efforts, it bursts through the front of the pu- 

 parium, and thus escapes from its prison. 1 



The insects of the Trichoptera order, or case-worm flies, 

 are quiescent when they first assume the pupa, but become lo- 

 comotive towards the close of their existence in that state. 

 Since they inhabit the water when they become pupae, Pro- 

 vidence has furnished them with the means of quitting that 

 fluid without injury, when they are to exchange it for the 

 air, which in their winged state is their proper sphere of ac- 

 tion. I have before described to you the grates which shut 

 up their cases when they become quiescent ; if they had no 

 means of piercing these grates, they would perish in the 

 waters. The head of these pupae is provided at first with a 



Lyonet, Trait. Anat. 15. 



