354 A COURSE ON ZOOLOGY. 



Fleas are apterous (wingless) insects, organized for 

 jumping, and having a mouth armed with small lancets 

 that are modified mandibles ; these lancets are enclosed 

 in a sheath formed by the union of the jaws. The bite 

 is painful because the insect secretes an irritating saliva. 



The bedbug is a hemiptera, and is still more objec- 

 tionable than the flea. It has one pair of rudimentary 

 wings, and when it is at rest the short beak is hidden in 

 a fold of the abdomen. The mandibles and the jaws 

 are modified into bearded needles, enclosed in a sheath 

 formed by the upper and lower lips. 



Among the parasitic arachnides may be classed the 



acarids or mites, crea- 



FIG. 317. '. . , 



tures having a discoid 



or globular body, and 

 a mouth ordinarily 

 adapted for sucking. 

 Among these are the 

 ticks, which attach 

 themselves firmly to the 

 skin of mammals by 



a, TromUdium holosericeum, female (mag- n f n qp rT . fl f pr j 



nifled 9 diameters) ; 6, larva, full grown means Ot a serrate ' 

 (harvest-bug). mouth formed by the 



union of the jaws. 



The harvest-bug or harvest-tick is the larva of an 

 acarid called trombidium. It has six feet, like the larvai 

 of most acarids, and is- found in the woods and fields 

 in July and August. It often occasions great incon- 

 venience to men, its presence in the skin producing 

 violent itching. 



The itch-insect, or sarcoptes scabiei, is hardly visible to 

 the naked eye ; the female lives in the skin of man and 

 of various animals, such as the ox, sheep, dog, etc., and 



