Insects, not having lungs, receive air into their bodies through holes in the skin. These are called spiracles. They are so protected by hairs within the holes that water will not enter them. This is why it is so difficult to drown an insect. But if you touch the abdomen of one of these skin-breathing creatures, for instance the yellow part of a wasp, with a drop of oil, the minute openings become almost immediately clogged and the insect falls dead as if choked completely. The skin consists of two layers, both of which are exceedingly interesting. The outer or scarf skin is called the cuticle on the outside of the body, while wherever the skin dips into the body it is modified into what is called mucous membrane. This outer skin is not what is rubbed off the surface in a Turkish bath manipulation or what is brought off by the rubbing one gives the body with a rough towel. These rubbings bring off merely the dead outer surface of the cuticle which should be out of the way because no longer useful. In man it continually wears off, in serpents it is shed annually in one slough. The cuticle is the portion of the covering of the body which may best be noticed when a blister has been raised in the skin. The blister is an accumulation of fluid between the cuticle and the true skin. The cuticle, or epidermis, is modified in many other ways than the one in which it becomes mucous membrane. Where the habits of the animal make warmth desirable the epidermis dips into the skin and without any break in its connection rises in the form of wool, which covers the body of the sheep so effectually. Where the animal is designed for flight there is the same characteristic dip into the material of the body, and out of the little sac so formed rises the feather which gives the bird its beauty and powers of flight. The feather is a modification of the scarf skin. Where protection is needed for the body beneath the surface of the water this changeable substance covers the true skin with hard scales that make the friction of the water as slight as possible, while giving a firm and light resisting surface to prevent wounds. Horns and hoofs are modifications of the scarf skin. Where claws or talons are needed in the business of fighting or tearing food in bits or digging holes in the ground or elsewhere, the scarf skin changes itself at the extremities of paws and feet and produces nails, talons, and claws, whose powers are both marvelous and varied. For the protection of most mammals the whole of the body is favored by this power of the scarf skin to produce whatever seems necessary for the comfort of the individual, and the body is indented with innumerable minute holes called hair follicles into which the scarf skin dips and rises again to the surface transformed into hairs of varying degrees of fineness and color, beautifully arranged in order, and all pointing in such directions as will add to the beauty or comfort or terrifying aspect of the animal.