Why have insects antenna or feelers?

Because the organ of touch is not generally distributed over the body, and the antennae are considered as appropriated to this sense. These organs are two or more in number, and are present in all the Crustacea and insects, but wanting in the arachnidae, or spider genus. They are situated on the head, usually between the eyes and the mouth. They consist of a number of joints, in general capable, by their flexibility, of examining the surface of a body. - Fleming.

Why are these antenna particularly necessary to insects?

Because of the insensibility of their outward coat, which is generally of a horny consistence; and also from their eyes being destitute, in most instances, of the power of motion.

The feelers of insects are better adapted for exploring the condition of the surfaces of bodies than any organ which we possess. But their sensibility of touch is limited to particular qualities, or confined within narrow bounds. The human hand, on the contrary, by its motions, the pliability and strength of the fingers, and the softness of the surface, is the most extensive and perfect organ of touch possessed by any animal. - Fleming.

Why have insects cushions on the under surface of their joints?

Because these cushions being either soft and smooth on the surface, or enlargements closely covered with short hairs, by their elasticity and resistance, aid the animal in climbing and leaping. They have likewise suckers, which, in all, are capable of being applied to the surface of a smooth body. By these means those insects which walk upon walls and trees, are enabled to overcome the resistance of gravitation.

Why does the mouth of Crustacea and some insects differ from that of red-blooded animals?

Because it is formed of two or more jaws placed laterally ; these move from without inwards, and, vice versa, whereas those of red-blooded animals move from above downwards, and back again. The parts which are termed the lips of insects, are two bodies; one of which is placed above or in front of the jaws, and the other below or behind them. The palpi (or short antennae) are articulated to the jaws. - Notes to Blumen-bactts Comp. Anat.

Why have all insects with jaws the power of masticating hard animal and vegetable substances?

Because these parts are of a firm, horny texture, and in many cases are very large, when compared with the size of the animal. The locust, the dragon-fly, the beetle, especially the stag-beetle, are examples in which the edges are very large and manifest, and often possess tooth-like edges.

Why does the sting of insects not only pierce the skin, but leave considerable pain?

Because the sting is hollow, and conveys the irritating or poisonous fluid within the wound, from a peculiar bag.

Why does the sting usually remain in the wound which it inflicts?

Because it is barbed at the sides of its point.