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Reptiles, or Amphibia: Insects

Insects appear as eggs hatched as a caterpillar or larva, which changes into a motionless chrysalis or nympha, the covering of which bursting, a butterfly evolves with wings, long-jointed legs, and two antennæ. Some have jaws, others no jaws; some have no wings, and others have four wings variously marked, and one order two wings. Insects have lymph instead of blood, and no bones, but hard coverings to which the muscles are attached. They have no vertebra. They do not breathe through the mouth or nostrils, but have air-vessels along their sides, called spiracula, and connected with other vessels called bronchiæ. They have the organs of sense, and make all the discriminations which accord with their physical power and wants. They are oviparous, but scorpions and aphides are viviparous. The male is always smaller and more colored than the female, who alone has stings, but males have horns. Genuine insects have 6 legs, a distinct head with 2 antennæ, and pores for respiration, connected with tracheæ in the sides. They are produced by eggs, and many pass through three metamorphoses after the egg state. The egg produces the larva, grub, or caterpillar, with 16 feet, 2 jaws, and 12 small eyes; this passes to the pupa chrysalis, and is then changed into the perfect insect, with 6 legs, and a proboscis, with eyes full of lenses. All insects-proper perform respiration by two air-pipes, or tracheæ, which run parallel through the body, and send off branches, and they inspire and expire by apertures in their sides. Their nervous system is two cords, which form ganglions. Their heads have two projecting antennæ, and they have 6 feet. They commence as larvæ, or worms, then change to chrysals or pupæ, and complete their being in various forms. Microscopic insects are generally in the larva state, and books and systems treat chiefly of the imago, or perfected insect.