LICE 345 



INSECTA 



The class Insecta has one pair of antennae, three pairs of mouth parts 

 (the fused labium being considered as one pair), and three pairs of legs. 

 They have three divisions of the body head, thorax, and abdomen. 



The head carries the antennae and mouth parts; the thorax, which is divided 

 into the pro meso and meta thorax, carries upon the ventral surface of each thoracic 

 segment a pair of legs and on the dorsal surfaces of the two posterior segments a 

 pair of wings. The abdomen does not support appendages. The air is supplied 

 by means of tracheae branching breathing tubes which have external openings or 

 stigmata. The tracheae are stiffened by spiral chitinous bands. The Malpighian 

 tubules are excretory organs of the alimentary system and excrete nitrogenous 

 waste material. Insects have two pairs of wings, the second pair of which is fre- 

 quently rudimentary and shows simply as knob-like projections. These are termed 

 halteres or balancers. In some insects both pairs of wings are rudimentary, as in 

 Siphonaptera. 



Where insects show metamorphosis we have voracious worm-like larvae coming 

 out of eggs; these larvse are succeeded by a quiescent no nf ceding encased pupa 

 which finally develops into an imago or fully developed insect. An insect which does 

 not present this developmental cycle shows incomplete metamorphosis. Of the 

 class Insecta only the Siphunculata, Rhynchota, Siphonaptera, and Diptera are of 

 special importance. 



SIPHUNCULATA (ANOPLURA) 



These are small dorso-ventrally flattened wingless insects not showing 

 metamorphosis. 



The Pediculidae 



In this family there are no wings and there is no metamorphosis. 

 The acorn-shaped eggs (nits) are deposited on hairs of the host. 



Pediculus capitis. The female is about % inch (3 mm.) long; the male 

 smaller. They vary in color according to the color of the hair of the host. The eggs 

 are deposited on the hairs of the head in number of 60 which hatch out in about six 

 days. The thorax is as broad as the abdomen. The male louse is rounded off 

 posteriorly and shows a dorsal aperture for a pointed penis, while the female is 

 recognized by a deep notch at the apex of the last abdominal segment. There seems 

 to be a marked preference exhibited by lice for their own peculiar racial host. It has 

 been suggested that this might account for certain peculiarities in infection where 

 different races were living together and under similar conditions as to food and 

 environment, and yet only one race contracts the disease (beriberi). The head louse 

 has been found to harbor leprosy bacilli when living on a leper. 



Pediculus vestimenti. This louse lives about the neck and trunk and deposits 

 its eggs in the clothing. They number about 75 and hatch out in three or four days 

 and become mature in about two weeks. Unlike the fleas there is no grub stage. 



