454 



ABTHROPODA. 



basal joints of the pedipaJpi, in which the chelicerae, either chelate, 

 clawed, or stylet-like, play. 



Since the mites are small and half or wholly parasitic, they are much 

 simplified in structure. Frequently heart and tracheae are lacking. The 

 larva as it escapes from the egg lacks the last pair of legs and then closely 

 resembles certain imperfectly segmented parasitic insects like the lice. 



The red mites or TROMBIDIID^E and the water mites, HYDRACHNID.E (Hy- 

 draclma* Atax *), are free-living in the adult condition, but parasitic as 

 young. The IXODID^: or ticks (Ixodes*}, live in woods or on bushes, attack 

 man and other mammals, burrowing beneath the skin, sucking the blood un- 

 til they become enormously swollen and fall off. The much smaller males 



FIG. 472. 



Fm. 473. 



FIG. 472. Sarcoptes scabei, female itch mite. (After Leuckart ) 



FIG. 473. Demodex folticulorum, follicle mite. (From Ludwig-Leunis.) 



are attached to the females and take no food. Argas persicus, of eastern 

 lands, with habits like a bedbug, is poisonous. The GAMASID^E are para- 

 sitic, species of Gamasus * occurring on beetles and Dermanyss-us* on bats. 

 The ACARID.E include permanent parasites like Sarcoptes scabei*' (fig. 472), 

 the cause of the 'itch,' and the closely allied cheese mite. The follicle 

 mite, Demodex folliculorum,* lives in the sebaceous glands of various 

 mammals, including man (fig. 473). 



Order III. Linguatulida. 



Elongate mites like Demodex lead to the Linguatulida, which 

 as adults live in the frontal sinuses of carnivorous mammals, as en- 

 cysted young in the liver of herbivorous forms, especially rodents. 

 The body is long, flattened and ringed, and hence somewhat tape- 

 worm-like (fig. 112). The adults have the mouth at the base of 

 a chitinous capsule, and on either side are two hooks regarded as 

 the claws of the first and second legs. Inside the body is a spa- 

 cious cavity traversed by the alimentary canal which is without 

 appendages. The nervous system is largely a circumcesophageal 



