HEXAPODA 



25 





Fig. 48. — Eggs of insects; 1, (Ecanthus nigricornis; 

 2, (Enis semidea; 3, Piezosterum subulatum; 4, Hydrometra 

 martini. 



is that the wings develop externally. That is, the wings of nymphs are 

 sac-like outgrowths of the body-wall which appear early and grow larger 

 as already explained. 



Complete metamorphosis. — Other insects, like the bees, butterflies, 

 moths, flies, and beetles leave the egg in an entirely different form from 

 that which they assume when 

 they reach maturity. A butter- 

 fly begins its active life as a 

 caterpillar. It feeds and grows, 

 and when full-grown changes to 

 a chrysalis. In this stage it 

 has very little resemblance to a 

 caterpillar. After a time there 

 bursts forth from the chrysalis 

 shell the butterfly, which looks 

 very little like the chrysalis and 

 still less like the caterpillar 

 from which it came. In a 

 similar way, from the egg laid 

 by a fly upon a piece of meat 

 there hatches, not a fly, but a 

 footless, worm-like maggot. 

 This when fully grown changes 

 to a quiescent object corres- 

 ponding to the chrysalis of a 

 butterfly. Later from this ob- 

 ject there escapes a winged fly like that which laid the egg. Those insects, 

 like the butterflies and flesh-flics which when they emerge from the egg 

 bear almost no resemblance in form to the adult insect, are said to un- 

 dergo a complete metamorphosis. In other words, the change of form 

 undergone by the insect is a complete one, and it passes through the fol- 

 lowing stages : — 



The egg. — This is the first stage in the existence of any insect, although 

 in some instances the egg remains in the body of the mother till it hatches. 

 But almost always the eggs are laid by the mother insect on or near the 

 food which gives nourishment to the young. Many of the most interest- 

 ing habits of insects are connected with the care of the eggs by the 

 parent. The eggs may have smooth oval shells; but often the shells are 

 beautifully ribbed and pitted (Fig. 48), and sometimes they are orna- 

 mented with spines, and are frequently exquisitely colored. 



The larva. — This is the second stage of an insect with a complete 



metamorphosis and is the form that 

 hatches from the egg. Familiar ex- 

 amples of larvae are caterpillars (Fig. 

 49), maggots, and grubs. In fact, many 

 creatures popularly known as worms 

 are larvae of insects. Away from the 

 ocean we find but few worms, except earthworms, leeches, "hair- 

 snakes," and worm-parasites in the intestines of men and animals. The 

 larval stage is devoted to growth; the sole business of a larva being 

 to eat and grow. All molting, because of increased size, is done in the 

 larval stage, later molts are simply for change of shape. 



Fig. 49. — A caterpillar, the larva of a moth. 



