Indeed the structure of an insect is entirely different from that of man or the quadrupeds, or any other vertebrate animal, and what we call head, thorax, abdomen, gills, stomach, skin, or lungs, or jaws, are called so simply for convenience, and not that they are made in the same way as those parts in the higher animals. An insect differs from a horse, for example, as much as a modern printing press differs from the press Franklin used. Both machines are made of iron, steel, wood, etc., and both print; but the plan of their structure differs throughout, and some parts are wanting in the simpler press which are present and absolutely essential in the other. So with the two sorts of animals; they are built up originally out of protoplasm, or the original jelly-like germinal matter, which fills the cells composing their tissues, and nearly the same chemical elements occur in both, but the mode in which these are combined, the arrangement of their products: the muscular, 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.]