THE CHARACTERS AND METAMORPHOSES OF INSECTS. 



into a quiescent state corresponding to the chrysalis state of the 



butterfly. Those insects which, like the grasshoppers, when they 



emerge from the egg resemble in form the adult arc said to undergo 



an incomplete metamorphosis. In other words, after leaving the egg 



they do not undergo a complete change of form. 



Moulting, Exiivice. — The body-wall of an insect is rendered more 



or less hard by the deposition within its cuticular 



layer of a horny substance known as chitine. 



The result of this hardening of the skin is to 



render it inelastic. Consequently as the body of 



an insect increases in size its skin becomes too 



small for it. When this occurs a second soft skin 



is formed beneath the outer hard one. Then the 



outer skin splits open, usually along the back, and 



the insect works itself out from it. The new skin 



being elastic accommodates itself to the increased 



size of the body. In a short time this new skin 



becomes hardened ; and as the insect grows, it in 



turn is cast off. This shedding of the skin is 



termed moulting or ccdysis. The cast skins are 



sometimes referred to as the exuvice. The number 



of moults varies greatly in the different groups of insects. In Fig. 



3 is shown the cast skin of a dragon-fly clinging to a reed. 



The Egg. — The egg is the first of the four principal stages through 



which an insect passes in the course of its development. In a few 



instances the egg is retained within the body of the female until 



after it is hatched ; in this case the in- 

 sect is said to be viviparous. An ap- 

 parent exception to the rule that all 

 ps* insects are produced from eggs is pre- 

 sented by certain generations of the 

 Plant-lice {Aphididce). This is discussed 

 in the description of that family. The 

 eggs of insects vary greatly in their 

 external characters. While many of 

 them are furnished with smooth oval 

 shells, in others the shells are beautiful- 

 ly ribbed, or pitted (Fig. 4), or furnished 



Fig 4 --Egg of Cotton-worm ^eatiy with spines or other appendages. There 



enlarged, (F rom the Author s Report l ■-"*.« m^^in-ici^^o. ^"'-1'- 



on cotton insects.) exists also in one end of the egz of an 



insect one or more pores known as mieropyles ; through these the 



Fig. 3. — Exuviae of a 

 Dragonfly. 



