. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. BODY LOUSE 389. species, which closes back like a finger against a thumbhke pro- jection of the next segment of the leg (Fig. 173). There are not even rudiments of wings. The body of a louse is clearly divided into head, thorax and abdomen (Fig. 174). The thorax is always broader than the head, a characteristic which distinguishes at a glance a true louse from the broad-headed bird louse (Fig. 172). The abdomen is divided into segments, six to eight of them in the human spe- cies; the terminal one is in
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. BODY LOUSE 389. species, which closes back like a finger against a thumbhke pro- jection of the next segment of the leg (Fig. 173). There are not even rudiments of wings. The body of a louse is clearly divided into head, thorax and abdomen (Fig. 174). The thorax is always broader than the head, a characteristic which distinguishes at a glance a true louse from the broad-headed bird louse (Fig. 172). The abdomen is divided into segments, six to eight of them in the human spe- cies; the terminal one is indented in the female, but is rounded in the male with the large spikelike copulatory or- gan often projecting at its tip (Fig. 174, p. 390). The digestive tract, as in most other blood-sucking insects, is furnished with capacious pouches branching from the stomach, which serve as food reser- voirs. The tracheal system is well developed and opens by prominent spiracles on the sides of the abdominal segments. Most species of lice are quite closely limited to a single host, and sometimes even genera are thus limited. Kellogg has suggested that the evolutionary affinities of different birds and mammals may be demonstrated by the kinds of lice which in- fest them. There are only three species which infest man, each selecting a different portion of his body as a habitat; these are the head louse, Pediculus capitis, the body louse, Pediculus humanus (vestmenti) and the crab louse, Phthirius pubis. The genus Pediculus is peculiar to man and the apes, with the ex- ception of one species which infests the monkey, Ateles. The genus Phthirius is represented only by the human species. Body Louse. — The body louse (Fig. 174) is by far the most common, as it is the most important, louse infesting man. It very closely resembles the head louse, but it is larger, more ro- bust and less active. Fertile offspring result from hybridization Fig. 173. Front leg of body louse, Pediculus humanus. Not
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