242 



MITES AND TICKS. 



any trace of segmentation ; it is confluent with the cephalothorax, the fusion between 

 the two being so complete, that, as in the harvest-spiders of the group Palpatores, 

 the anterior sternal plates of the abdomen are thrust far forward between the 

 coxae of the cephalothoracic limbs. As in all Arachnida, the mouth is adapted for 

 sucking, but the jaws are often partially united, and form, with a plate termed 

 the epistome, and the labium, a beak. The epistome is often of large size, and is 

 attached to the front border of the carapace ; the mandibles are either pincer-like 

 or simply pointed at the tip, forming piercing organs. The palpi, which resemble 

 a pair of small legs, have their basal segments, or maxillae, united together and to 

 the labium, to form a conspicuous plate or hypostome, constituting the floor of the 

 mouth. These organs forming the mouth-parts are often separated from the rest 

 of the cephalothorax by a membranous joint, and constitute a kind of movable 

 head, the capitulum. In many cases there are no traces of special respiratory 

 organs, breathing being effected by means of the skin ; but, when present, such 

 organs take the form of tracheal tubes, the apertures of which vary in position. 

 They may, for instance, lie in the head between the mandibles and palpi, or far 

 back in the body at the base of the legs of the last pair; but in some species 

 they occupy intermediate positions, and open in front either of the first, second, 

 or third legs. Another character of some value 'in separating the ticks from the 

 harvest-spiders, is that in the former the young undergo a metamorphosis in the 

 course of growth, being hatched from the egg as six-footed larvae, which later 

 acquire the fourth pair of legs. The order may be divided into the typical mites 

 and ticks (Acarina), and an aberrant worm-like group (Vermiformia). 



The Acarina include a number of families severally distinguished by the 

 position of the respiratory stigmata, and the form of the mandibles and palpi. In 

 the velvety mites (Trombidiidw) the integument is soft and covered with variously 

 coloured hairs ; the legs are adapted for walking or running, the mandibles are 



pointed at the tip, and the stigmata open in the 

 anterior portion of the body. There is usually 

 a pair of eyes on the carapace, although these 

 may be wanting. These mites, which may be 

 either parasitic or leading a free life, feed by 

 sucking the juices of animals or plants. A 

 fairly common British species is Trombidium 

 holosericeum, the second name referring to the 

 clothing of crimson silky hairs covering its body. 

 In the six -footed larval stage these mites live 

 parasitically upon harvest-spiders, to which they 

 cling, and resemble a cluster of bright red beads. 

 Before attaining maturity they fall from their 

 host to the ground, where, after undergoing their 

 final moult, they lead a free wandering life, living 

 upon minute insects such as aphides. In tropical countries mites of this genus reach 

 a large size, measuring half an inch in length. They are beautiful and striking 

 objects, resembling tufts of bright blood- red plush. 



Nearly allied are the spinning-mites {Tetranychidce), which live exclusively 



velvety mite, Trombidium holosericeum, 

 from below (enlarged eight times ; nat. 

 size on the leaf). 



