Inside the egg wonderful changes soon commence, and their consummation is a tiny larva. Somewhat similar changes can be easily and most profitably studied by breaking and examining a hen's egg each successive day of incubation. As with the egg of our own species and of all higher animals, so, too, the egg of insects, or the yolk, the essential part--the white is only food, so to speak--soon segments or divides into a great many cells, these soon unite into a membrane--the blastoderm--and this is the initial animal. This blastoderm soon forms a single sack, and not a double sack, one above the other, as in our own vertebrate branch. This sack, 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 incorporations within the eggs of the germ cells from the male, which enter the eggs at openings called micropyles. 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, too, which an insect may produce, is subject to wide variation. Some insects produce but one, two or three, while others, like the queen bee and white ant, lay thousands, and in case of the ant, millions. [Illustration: Fig. 12. _Larva of Bee._] THE LARVA OF INSECTS. From the egg comes the larva, also called grub, maggot, caterpillar, and very erroneously worm. These are worm-shaped (Fig. 12), usually have strong jaws, simple eyes, and the body plainly marked into ring divisions. 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 caterpillars--have only four or six, while the larvæ 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 larvæ of insects are voracious eaters--indeed, their only work seems to be to eat and grow fat. As the entire growth occurs at this stage, their gormandizing habits are the more excusable. I have often been astonished at the amount of food that the insects in my breeding cases would consume. The length of time which insects remain as larvæ is very variable. The maggot revels in decaying meat but two or three days; the larval bee eats its rich pabulum for nearly a week; the apple-tree borer gnaws away for three years; while the seventeen-year cicada remains a larva for more than sixteen years, groping in darkness, and feeding on roots, only to come forth for a few days of hilarity, sunshine, and courtship. Surely, here is patience