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- 

 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, TronMdium holosericeum, female (mag- f ^PrratpH 



nifled 9 diameters); 6, larva, full grown r 



(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 Iarva3 

 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 



