ORDERS OF INSECTS.
The fifth class of Linnæus comprised the Insects; and the branch of Zoology which treats of them is called Entomology. Nearly all insects go through certain great changes at different periods of their existence. From the egg is hatched the larva, which is a grub or caterpillar, and destitute of wings; this afterwards changes to a pupa, or chrysalis, wholly covered with a hard shell, or strong skin, from which the perfect or winged insect bursts forth. Spiders and their allies, which were included by Linnæus in the insects, issue from the egg in nearly a perfect state.
Linnæus divided his class of insects into seven Orders:
I. Coleopterous.—Having elytra, or crustaceous cases covering the wings; and which, when closed, meet in a straight line along the middle of the back, as the cockchafer.
II. Hemipterous.—Having four wings, the upper ones partly crustaceous, and partly membranous; not divided straight down the middle of the back, but crossed, or incumbent on each other, as the cockroach.
III. Lepidopterous.—Having four wings covered with fine scales almost like powder, as the butterflies and moths.
IV. Neuropterous.—Having four membranous and semi-transparent wings, veined like network; and the tail without a sting, as the dragon-fly and ephemera.
V. Hymenopterous.—Having four membranous and semi-transparent wings, veined like network; and the tail armed with a sting, as the wasp and bee.
VI. Dipterous.—Having only two wings, as the common house-flies.
VII. Apterous.—Having no wings, as the spiders.