LICE. 229 



kindgom. Besides the classes Insecta and Arachnoidea, we have the 

 Crustacea (crabs, lobsters) and the Myriapoda (centipedes, etc.). The 

 two latter are of very little importance medically. The Arthropoda 

 have segmented bodies, but they differ from the worms in having 

 jointed appendages for the purposes of taking in food and moving from 

 place to place. They also have an exoskeleton which is more or less 

 unyielding from the deposit of chitin in the cuticle. 



The class Insecta have one pair of antennae, 3 pairs of mouth parts 

 (the fused labium being considered as one pair), and 3 pairs of legs. 

 They have 3 divisions of the body head, thorax and abdomen. The 

 air is supplied by means of tracheae branching breathing tubes. 

 Insects have 2 pairs of wings, the second pair of which is frequently 

 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 the Aphaniptera. Of the class Insecta only the 

 Rhynchota (Hemiptera) and the Diptera are of special importance. 



RHYNCHOTA. 



The Rhynchota are sucking insects in which the lower lip forms a 

 long thin tube or rostrum which can be bent under the head or thorax. 

 Inside this tube are biting parts mandibles and maxillae. 



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 1/12 of an inch 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. The 

 thorax is as broa'd as the abdomen. There seems to be a marked 

 preference exhibited by lice for their own peculiar racial host. It has 

 recently been suggested that this might account for certain peculiari- 

 ties 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.) 



Pediculus vestimenti. This louse lives about the neck and trunk 



