TEE MITES. 



341 



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

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



Order 4. Acarina. — Tlie mites are degenerate Arach- 

 iiida, tlie body being oval in form, 

 the head usnully small, more or 

 less merged witb the thorax, wliile 

 tlie latter is not differentiated 

 from the abdomen. There is a 

 •slight metamorphosis, the mite 

 when first hatched having but. 

 three pairs of legs, the fourth 



Fig. 312.— Sugar-mite. Much 

 enlarged. 



Fig. 313. — Carolina scorpion {Buthua 

 Carolinianus). Namral 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 albi- 

 pictusViick). Closely allied to this is 

 Ixodes bovis Riley, 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. 

 313, 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 

 Tinder the epidermis of the leaves of 

 trees, often forming galls. 



des. 



. SU.—Chelifer cancroi- 

 Magnified. 



