244 



MITES AND TICKS. 



and the legs are adapted for walking or running. The species figured (Gamasus 



coleoptratorum) may often be seen in numbers attached to the lower side of dor- 

 beetles. Others live parasitically upon bats and birds, one of the commonest 



being Dermanyssus avium, which infests poultry, canaries, and other cage-birds, 



whence they sometimes migrate to the persons who have charge of them. Ceylon, 



Sumatra, and Mauritius are the habitat of Holo- 

 thyrus, in which the body is hard and horny, like 

 that of a beetle, and of a shining chestnut colour. 



Of all the Acari the best known and most 

 troublesome are those belonging to the family Ixodidce, 

 which infest terrestrial vertebrates, and sometimes 

 attach themselves to men. They are furnished with 

 a longish cylindrical beak, armed with recurved 

 hooks, and formed by the two mandibles above and 

 the long slender labium below. The palpi are either 

 free, as in Argas, or closely applied to the beak, 

 forming in fact a sheath for it, and preventing the 

 escape of blood, which flows from the puncture made 

 by the beak. In the accompanying figure, showing 

 the mouth - parts of the common English dog- or 

 sheep-tick (Ixodes ricinus), the lower surface of the 

 capitulum, or head-like process, which bears the beak 

 is shown at c ; d, e, f, g, represent the four segments 

 of the palpi ; h is the labial process armed with the 

 hooks forming the lower side of the beak; and i 

 indicates the tips of the two mandibles, forming its 

 upper side, and projecting beyond the apex of the 



labium. By means of this beak, which is thrust to its 



base into the integument, the tick adheres firmly to its 



host, and in detaching them care must be taken that the 



head be not left behind buried in the skin. The species 



/. ricinus is commonly found in all stages of growth (see 



a, b, c, d, e, f of figure) adhering to cattle. The females 



pump themselves full of blood, and swell up to the size of 



a large pea; but the male — formerly regarded as a distinct 



species under the name Reduvius — is of smaller size, and 



resembles the empty female in shape. In distribution 



these pests are almost cosmopolitan, but in tropical 



countries they reach much greater dimensions than in 



temperate climes, the females sometimes attaining the 



size of a large gooseberry. In addition to mammals, 



they attack birds, tortoises, snakes, and lizards ; and even 



the thick hide of the hippopotamus and rhinoceros is of 



no avail against attack. On account of their numbers, 



the effects they produce upon cattle are sometimes of a 



serious nature. These ticks are not, however, found 



MOUTH-ORGANS OF SHEEP-TICK. 



c, Capitulum ; d, e, f, g, Segments of 

 palp ; i, Spiny - beak, formed by 

 fused mandibles. 



ENGLISH SHEEP-TICK. 



Six -legged young; b, Eight- 

 legged young ; c, Male ; d, 

 Female not distended ; e, 

 Female distended with blood 

 from below ; /, Same from 

 above ; g, Specimen clinging 

 to the hairy integument of 

 a mammal. (All figures en- 

 larged twice.) 



