78 Second Stage of Insects. 



double arch, one above the other, as in our own verte- 

 brate branch. This sac, looking like a miniature bag 

 of grain, grows by absorption, becomes articulated, and by 

 budding out is soon provided with the various members. 

 As in higher animals, these changes are consequent upon 

 heat, and usually, not always, upon the incorporation within 

 the eggs of the sperm cells from the male, which enter 

 the egg at an opening called the micropile. The time it takes 

 the embryo inside the egg to develop is gauged by heat, 

 and will, therefore, vary with the season and temperature, 

 though in different species it varies from days to months. 

 The number of eggs which an insect may produce is sub- 

 ject to wide variation. There may be a score; there may 

 be thousands. 



THE LARVA OF INSECTS. 



From the e.^^ comes the larva, also called grub, maggot, 

 caterpillar, and very erroneously worm. These are worm- 

 shaped (Fig. 24), usually have strong jaws, simple eyes, 

 and the body plainly marked into ring divisions. In some 

 msects there are fourteen of these rings or segments, or teii 

 beside the head and three rings of the thorax. In bees and 

 nearly all other insects (Fig. 34, /") there is one less abdomi- 

 nal ring. Often, as in case of some grubs, larval bees, and 

 maggots, there are no legs. In most grubs there are six legs, 

 two to each of the three rings succeeding the head. Besides 

 these, caterpillars have usually ten prop-legs farther back on 

 the body, though a few — the loopers or measuring caterpil- 

 lars — have only four or six, while the larvae of the saw-flies 

 have from twelve to sixteen of the false or prop-legs. The 

 alimentary canal of larval insects is usually short, direct, 

 and quite simple, while the sex-organs are slightly if at all 

 developed. The larvae of insects are voracious eaters — 

 indeed, their only work seems to be to eat and grow fat. 

 This rapid growth is well shown in the larva of the bee 

 which increases during its brief period from egg to full 

 grown larva — less than five days — from 1200 to 1500 times 

 its weight. As the entire growth occurs at this stage, their 

 H'ormandizing habits are the more excusable. I have often 

 been astonished at the amount of food that the insects in 



