. 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 chelicerse 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 chelicerse 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-. FiG. 152. Hypostomes of ticks; A, ear tick, Otiobius (or Omithodorus) megnini, nymph; B, Argas persicm, adult; C, Ixodes tem of tracheSB which Open ricinits, adult female; D, same, male; E, Ixodes vespertilionis, adult female; F, same, male; G, Omithodorus mouhata, nymph; H, Omithodorus savignyi, adult. (A, after Sal- mon and Stiles; others after Nuttall.) by a pair of spiracles in the vicinity of the fom-th 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. — AH ticks are parasitic during some part of their Hves. The majority of them infest mammals, though many species attack birds and some are found on cold- blooded animals. A very d
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