THE MITES. 



341 



pairs of short-clawed feet. Pentastoma (Fig. 309) occurs in 

 the lungs and liver of man, and in horses and sheep. 



Order 4. Acarina. The mites are degenerate Arach- 

 nida, the body being oval in form, 

 the head usually small, more or 

 less merged with the thorax, while 

 the latter is not differentiated 

 from the abdomen. There is a 

 slight metamorphosis, the mite 

 when first hatched having butj 

 three pairs of legs, the fourth 



Fig. 312. Sugar-mite. Much 

 enlarged. 



Fig. 313. Carolina scorpion (Buthus 

 Carolinianus). Natural size. 



(and last) pair being added after a moult. A typical mite, 

 though above the average size of the members of the group, 

 is the tick (Fig. 310, Ixodes alU- 

 pictusPack). Closely allied to this is 

 Ixodes bovis Eiley, the cattle-tick 

 (Fig. 311), which buries its head in 

 the skin, anchoring itself firmly by 

 means of the backward -pointing teeth 

 of its jaws. Other examples of mites 

 are the cheese and sugar mites (Fig. 

 312, Tyroglyphus sacchari). The lat- 

 ter appear as white specks in sugar, 

 and to them is due the disease known 

 as grocers' itch. Certain mites live 

 under the epidermis of the leaves of 

 trees, often forming galls. 



Fig. SU.Chelifer cancroi- 

 des. Magnified. 



