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 are said to undergo 

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

 they do not undergo a complete change of form. 



Moulting, Exuvicz. 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 



o 



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 ecdysis. The cast skins are 



6 FIG. 3. Exuviae of a 



sometimes referred to as the cxfivice. The number Dragon-fly. 



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 

 insects are produced from eggs is pre- 

 sented by certain generations of the 

 Plant-lice (Aphidida). 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 

 with spines or other appendages. There 

 exists also in one end of the egg of an 

 in ct one or m$re pores known as mlcropyles ; through these the 



FIG. 4. Egg of Cotton-worm, great! 

 enlarged. (From thd Author's Kepo 

 on Cotton Insects.) 



ready 

 rt 



