cular, nervous and skin tissues, differ in the
two animals. The plan of structure, namely, the form and arrangement of
the body walls, the situation of the appendages to the body, and of the
anatomical systems within, i.e., the nervous, digestive, circulatory,
and respiratory systems, differ in their position in relation to the
walls of the body. Thus while the two sorts of animals reproduce their
kind, eat, drink and sleep, see, hear and smell, they perform these acts
by different kinds of organs, situated sometimes on the most opposite
parts of the body, so that there is no comparison save in the results
which they accomplish; they only agree in being animals, and in having a
common animal nature.

[Illustration: 4. Different forms of jaws.]

[Illustration: 5. Mouth parts of the Larva of a Beetle.]

[Illustration: 6. Maxilla of a Beetle.]

_How Insects Eat._ The jaws of insects (Fig. 4) are horny processes
situated on each side of the mouth. They are variously toothed, so as to
tear the food, and move horizontally instead of up and down as in the
horse. The act of taking the food, especially if the insect be
carnivorous in its habits, is quite complex, as not only the true jaws,
but the accessory jaws (maxillae, Fig. 5, _a_, upper, b, under side of
the head of a young beetle; _at_, antennae, _md_, mandible, _mx_,
maxillae, _mx_[1], labium) and the feelers (palpi) attached to the
maxillae, and the under lip (labium) are of great service in enabling the
insect to detect its food both by the senses of touch and smell. The
maxillae are in the fully grown beetle (Fig. 6) divided into three lobes,
the outermost forming the palpus, and the two others forming sharp
teeth, often provided with hairs and minute brushes for cleansing the
adjoining parts; these strong curved teeth are used in seizing the food
and placing it between the grinders, where it is crushed, prepared for
digestion and swallowed. Fig. 7 represents the mouth parts of the humble
bee. (_b_, upper lip; _d_, mandible; _e_, maxilla; _f_, maxillary
palpus; _g_, tongue; _ih_, labium and tabial palpi; _k_, eye.)

[Illustration: 7. Mouth parts of a Humble Bee.]

The alimentary canal passes through the middle of the body, the stomach
forming usually a simple enlargement. Just before the stomach in certain
insects, as the grasshopper, is a gizzard armed with rows of powerful
horny teeth for finely crushing grass.

Insects eat almost incredible quantities of food