. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 354 TICKS Most ticks have a little shield or " scutum " on the dorsal sur- face, quite small in the females, but nearly or quite covering the back in the males (Fig. 156). Attached to it in front is a little triangular piece, the capitulum or " head " which bears the mouthparts (Fig. 150). The latter consist of a quite formidable piercing organ, the hypostome, a pair of chelicerae or mandibles which are armed with hooks (Fig. 151), and a pair of blunt palpi which are probably tactile
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 354 TICKS Most ticks have a little shield or " scutum " on the dorsal sur- face, quite small in the females, but nearly or quite covering the back in the males (Fig. 156). Attached to it in front is a little triangular piece, the capitulum or " head " which bears the mouthparts (Fig. 150). The latter consist of a quite formidable piercing organ, the hypostome, a pair of chelicerae or mandibles which are armed with hooks (Fig. 151), and a pair of blunt palpi which are probably tactile in function. The hypostome is a rasplike structure, beset with row after row of recurved teeth (Fig. 152). So firmly do these hold in the flesh into which the proboscis is inserted that forcible removal of a tick often results in the tearing off of the body from the capitulum which remains at- tached to the host. Like other Arachnida, ticks have four pairs of legs. These are quite conspicuous when the body is empty but are hardly noticeable after en- gorgement. The breathing apparatus consists of a sys- tem of tracheae which open by a pair of spiracles in the vicinity of the fourth pair of legs. The shape of the plates which cover the spir- acles are sometimes used in distinguishing species. The ventral surface has two openings, the genital pore just back of the pro- boscis, and the anus some distance from the posterior end of the body (Fig- 154). Habits and Life History. — All ticks are parasitic during some part of their lives. The majority of them infest mammals, though many species attack birds and some are found on cold- blooded animals. A very decided host preference is shown by some species, whereas others appear to be equally content with any warm-blooded animal which comes their way. In many species the hosts or parts of hosts selected by the adults are not the same as those selected by the immature Fig. 152. Hypostomes of ticks; A, ear tick, Otiobius (or Or
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmedical, bookyear1918
