LOUSE, a small parasitic insect of a family (Pediculiche) of doubtful affinities, but usually considered to be Hentiptera, much de graded through long-continued parasitism. The lice are all of small size, have soft, much flat tened bodies with thin integument, the ab domen enlarged, the thorax indistinctly seg mented and without the slightest trace of wings, and the short legs terminated with strongly hooked, stout claws. The mouth-parts are adapted for sucking. There is a short proboscis provided with hooks, from the centre of which, when fixed in the skin of the host, protrudes an extremely delicate tube. The head is also provided with a pair of short, three- or five-jointed antenna, and small simple eyes. Probably on account of their disgust ing habits the lice have been but little studied, and beyond the fact of their parasitism very little is known of their habits. They feed ex clusively upon blood, which is secured by wounding the host's skin, fixing the proboscis by means of its hooks, and Inserting the delicate tube above mentioned in the wound. A suction-bulb in the head propels the blood through the long writhing oesophagus into the bilobed stomach. Lice never leave their host
except to pass to another, and the eggs, as well as all stages of the young, are found with the adult. Only six genera and less than 50 species have been described, but probably many others remain undiscovered. They are found on mammals exclusively, each species of mammal commonly harboring a peculiar species of louse. Man is more richly endowed, having three species: the head-louse (Pediculus capitis), the body-louse (P. corporis) and the crab-louse (q.v.). The two first mentioned are very closely alike and are said to vary according to the different races of men which they infest. Human lice are of course associated with filth, and are found only upon neglected children and persons of uncleanly habits. A very re markable louse is found on the seal, and is consequently aquatic.
The bird-lice (q.v.), or Mallophaga, are en tirely distinct from the true lice.
Consult Piaget,