II. ACERATA: LINGUATULIDA 



397 



into a sucking beak. This consists of a tube formed by the basal joints of the 

 pedipalpi, 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 trachea 1 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 (TROMBIDIID/E) and water mites, HYDRACHXID/E (Hydrachna* 

 A tax*}, are free-living as adults, but parasitic as young. The IXODID.F. or ticks 

 (Ixodes*), attack man and other in immals, burrowing beneath the skin, sucking 



FIG. 430. FIG 431. 



FIG. 4^0. Sarcoptes scabei, female itch mite (after Leuckart). 

 FIG. 431. Demodex folliculorum, follicle mite (from Ludwig-Leunis). 



the blood. Their relation to disease is referred to on p. 190. The much smaller 

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

 lands, with habits like a bedbug, is poisonous. GAMASID.E, parasitic, Gamasus* 

 on beetles, Dermanysyus* on bats. The ACARID,*: include permanent parasites 

 like Sarcoptes scabei* (fig. 430), the cause of the 'itch,' and closely allied cheese 

 mite The follicle mite, Demodex folliculorum* lives in the sebaceous glands 

 of various mammals, including man (fig. 431). 



Order III. Linguatulida. 



Elongate mites like Demodex lead to the Linguatulida, which as adults live 

 in the frontal sinuses of carnivorous mammals, as encysted young in the liver of 

 herbivorous forms, especially rodents. The body is long, flattened and ringed, 

 and somewhat tapeworm-like (fig. 113). 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 spacious cavity traversed by the ali- 

 mentary canal which is without appendages. The nervous system is largely a cir- 

 cumoesophageal ring; the sexual organs are very complicated, the males having 

 the openings in front, the females at the hinder end. The presence of these para- 

 sites causes a profuse catarrh, and the eggs pass out with the mucus. Falling on 

 vegetation, these are liable to be eaten by various animals. The larvie (fig. 43 2 ) 

 have a boring apparatus in front and two pairs of legs, the latter lost in the 

 metamorphosis except for the hooks. It is by no means certain that these arc 

 degenerate arachnids. Pentastonntm. 



Usually associated with the Arachnida are two other groups of very doubtful 

 position, which until more definite knowledge is obtained, may remain near them. 



