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Rh reduced to as few as two bristles on the lips. The term "hair," however, is apt to be somewhat loosely applied; it has been made use of to describe, for example, the slender processes of the chitinous skin of the Crustacea. It will be necessary, therefore, to enter into the microscopical structure and development of the mammalian hair. Hair is found in every mammal. The first appearance of a hair is a slight thickening of the stratum Malpighii of the epidermis, the cells taking part in this being