Body flattened. Legs adapted for climbing among hairs and feathers, as the last joint of the foot is hook-shaped, and can be bent back against the preceding joint; a hair can thus be held fast between the two joints. Eyes absent or ill developed (simple). Wingless. The eggs (“nits”) are fastened by the mother louse to the hairs of the host; the young lice resemble the old ones in almost all particulars; there is no true metamorphosis. All lice have a kind of proboscis, which can be protruded and retracted, and upon which are placed the mouth-parts, which enable it to be used for sucking or biting. According to the last feature a distinction can be drawn between true or blood-sucking lice and biting lice or fur-eaters, which devour small scales derived from the skin or else bits of hair and feathers. Lice multiply very rapidly on the bodies of human beings and animals when insufficiently cleansed, and under these circumstances more on sick and ill-nourished individuals than on those which are healthy and well nourished. It is obvious that the true, blood-sucking lice usually injure their host more than the biting lice, which, however, especially when present in large numbers, may cause an intolerable and injurious itching by their movements here and there. _Preventive Measures_: Suitable feeding and treatment. Proper care of the skin. _Remedies_: Repeated combing with a comb which has been dipped into a solution of soda. Rubbing the badly infested spots with soft soap and soda, washing them out after twenty-four hours. Among other washes are—6 parts soft soap, 1 part benzine, 10 to 15 parts water; or tobacco water, 1 part of common tobacco in 20 to 25 parts water; arsenious acid, in various mixtures, _e.g._ in Bigg’s Composition (p. 193). Employ the muzzle. [Illustration: FIG. 122.—Horse Louse (_Hæmatopinus macrocephalus_), magnified ten times. ] CLASS II.: =MYRIOPODA= (CENTIPEDES AND MILLIPEDES). Respiration by tracheæ, as in insects. The body consists of a head and a large number of very similar segments, each of which possesses limbs. One pair of antennæ. This class is divided into two orders: (1) that of =Centipedes= (_Chilopoda_), with mouth-parts adapted for seizing prey, and _one_ pair of legs to each segment; (2) that of =Millipedes= (_Chilognatha_), adapted for devouring substances resembling humus, also the parts of plants; and _two_ pairs of legs to each segment. Here belong, above all, the =Snake Millipedes= (_Julus_) or “False Wireworms” (Fig. 123), of which several species eat out germinating seeds (peas, beans, mangolds, and beet), and also attack juicy plant parts (potatoes, turnips, carrots). Seedlings may be protected by using potatoes to draw away the millipedes. [Illustration: FIG. 123.—Common Snake Millipede (_Julus terrestris_), somewhat magnified. ] CLASS III.: =ARACHNOIDEA= (SCORPIONS, SPIDERS, MITES).