ACARI, OR MITES ; RICINI^E, OR TICKS. 



229 



FIG. 452. ACARUS DO- 

 MKSTJCUS, or CHEESE- 

 MITE, magnified. 



many Beetles which feed upon decaying substances, are entirely 

 covered by them. The Acari, or True Mites, 

 have the legs adapted for walking; and 

 some of them are of active habits. The com- 

 mon Cheese-Mite is familiar to every one ; 

 and there are many other species which 

 nearly resemble it in structure and habits, 

 but which feed upon different substances. To 

 this group belongs a small species, which appears to be the 

 occasion of one of the most disgusting diseases of the skin, the 

 itch. It is scarcely visible to the naked eye ; but when exa- 

 mined under the microscope, it is seen to have an oval body ; a 

 mouth of conical form, armed with 

 several bristles; and eight feet, of 

 which the four anterior are terminated 

 by small suckers, that enable it to 

 adhere firmly to any solid bodies, 

 whilst the four posterior are termi- 

 nated only by bristles. Some of this 

 Acari have the power of spinning 

 webs, and are commonly ranked with 

 the Spiders ; one of these is well- 

 known as the Red Spider in hot- 

 houses, where it greatly injures the 

 plants by covering the leaves with 

 its webs. The Ricinice, commonly 

 known as Ticks, are usually desti- 

 tute of eyes, but have the mouth 

 provided with lancets, that enable them to penetrate more readily 

 the skins of animals whose blood they suck. They are usually 

 of a flattened, round, or oval form ; but they often acquire a 

 very large size by suction, and become distended like a blown 

 bladder. They are found in thick woods, abounding in brushwood, 

 briars, &c., and attaching themselves to plants with the two 

 fore legs. They fasten upon dogs, cows, horses, and other 

 quadrupeds, and even upon the tortoise ; and they bury their 

 suckers (which are often furnished with minute recurved hooks, 



FIG. 453. SARCOPTES SCABIEI, or 

 ACARUS OF THE ITCH. 



