Genus. Pediculus, Linnæus.
Pediculus capitis, de Geer, 1778.
Fig. 374.—Mouth parts of Pediculus vestimenti. Enlarged. (After Denny.)
Fig. 375.—Ovum of the head louse. 70/1.
Male 1 to 1·5 mm. in length, female 1·8 to 2·0 mm. in length. The colour varies from light grey to black according to the colour of the hair of the human race upon which they are parasitic. The abdomen has eight segments, of which the six central ones are each provided with a pair of stigmata. The thorax is as broad as the abdomen. Eggs 0·6 mm. in length; about fifty are deposited by a female head louse. The young can propagate when eighteen days old.
The head louse lives especially in the hairy parts of the head of human beings; more rarely it is found on other hairy parts of the body. It is spread over the entire surface of the globe, and was present in America before the arrival of Europeans. Quite exceptionally it is said that it bores itself deep into the epidermis and can live in ulcers.