THE MITES AND TICKS 3209 



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 characteristic 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 ( Trombidiidce) the integument is soft and covered with variously 

 colored 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 ma5 r 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 VEI < VETY MITE ' Trombidium holoseri- 



ceum, FROM BEI.OW (enlarged eight 

 host to the ground, where, after undergoing their times . natural size on the leaf)- 



final molt, 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 

 upon plants, and obtain nourishment by sucking the sap. One of the best known 

 is Tetranychus telarius, a little red mite, sometimes called the money spider. The 

 web it spins is of very fine texture, and may usually be found on the backs of 

 leaves, where it appears to be merely used as a protective screen for both adults 

 and young. The silk is secreted from a conical nipple situated on the under side of 

 the extremity of the abdomen, and, as in the case of spiders, is manipulated by the 

 appendages. Also related to the Trombidndce, but connecting them with the next 

 family, is the common mud mite, Lhnnochares , which lives in fresh-water ponds, 



