20 THE SKIN OF INSECTS. 



THE SKIN, OR CRUST, OF INSECTS. 



IT seems indispensable to every plant and every 

 animal to have a skin, to cover and protect the more 

 sensible parts in the interior of the body. The skin 

 in insects, however, appears still more important, from 

 its having to fulfil, in some degree, the office of the 

 bones in other animals. 



The skin, therefore, is usually hard, like horn, or 

 tough, like leather or parchment; though in some 

 species, and also in the first stage of a very considera- 

 ble number, it is thinner and softer than the human 

 scarf skin. 



In all cases, the skin furnishes a series of levers, or 

 points of attachment and support to the muscles, by 

 which every motion of the insect must be made. Un- 

 like the skin of animals, therefore, that of insects is 

 made up of various pieces, more or less closely jointed 

 or joined like the various bones of animals. Each 

 bone of other animals, moreover, is well known by a 

 distinct name ; but the pieces of the skin in insects 

 have only been recently examined, and the few names 

 already given to the pieces are not well determined, 

 and still in much confusion. 



A talented French naturalist, M. Audouin, thinks 

 he has reason to conclude that there is always, from 

 the moment of exclusion from the egg, a determinate 

 number of pieces in every insect, probably thirteen, 

 which are either distinct or two or more of them 

 united ; that various species differ in having some of 

 the pieces large and others small, or altogether want- 

 ing ; and that when any piece is found larger, other 

 pieces near it will be proportionably smaller. 



The human skin is formed of three layers, the scarf 



