96 GENERAL ZOOLOGY 



ing to the race upon which it is found. It is very common 

 in many tropical countries where the natives may often 

 be seen searching through each others heads for the para- 

 sites. The female head louse lays about fifty eggs, attached 

 to hairs. Pediculus corporis, the body louse, is larger than 

 the head louse. It is gray in color and hence is known in 

 some localities as the "gray-back." This louse causes 

 much irritation, crawling over the body and inflicting 

 painful bites. The eggs are laid in the seams of garments. 

 The young lice or the adults may be active in discarded 

 clothing. The crab-louse, Phthirius inguinalis, is found 

 among the hairs of the pubic region, eyelashes, eyebrows, 

 and sometimes on other parts of the body where it causes 

 irritation, eruption, and discoloration of the skin. It 

 attaches its eggs to hairs. 



Though fleas are the chief carriers of the bubonic plague, 

 lice may transmit the disease and have also been suspected 

 of carrying leprosy. Lice are of chief interest, however, as 

 the proven carriers of typhus, a fatal febrile infection of 

 unknown cause. Body lice of course thrive most when 

 people are filthy. The terrible outbreaks of typhus fever 

 in Mexico and Serbia, following the advent of war, were due 

 to poverty and uncleanliness among a rather ignorant 

 population. The chief means used in fighting these great 

 epidemics were simple sanitary measures which would kill 

 or prevent the breeding of lice i.e., boiling clothes regularly, 

 fumigation of public conveyances, and the use of blue 

 ointment, paraffin oil, or kerosene on the surface of the body. 



Suborder 2. Homoptera (Fig. 47). Hemipterous in- 

 sects with four similar membranous wings; the mouth 

 parts form a jointed beak which arises from posterior ventral 

 part of the head. Many insects of great economic impor- 

 tance belong here scale insects, plant lice, cicadas, tree- 

 hoppers, spittle insects, etc. All these obtain their food 

 by burying their beaks in plants and sucking the sap. The 

 three following families are of particular importance: 



Aphidce, plant lice or aphids. These little insects are 



