HEMIPTERA. 217 



3. Bark-lice. CoccidcB. 

 The celebrated scarlet in grain, which has been employed 

 in Asia and the South of Europe, from the earliest ages, as a 

 coloring material, was known to the Romans by the name of 

 Coccus, derived from a similar Greek word, and was, for a 

 long time, supposed to be a vegetable production, or grain, as 

 indeed its name implies. At length it was ascertained that 

 this valuable dye was an insect, and others agreeing with it in 

 habits, and some also in properties, having been discovered, 

 Linnreus retained them all under the same name. Hence in 

 the genus Coccus are included not only the Thola of the Phoe- 

 nicians and Jews, the Kermes of the Arabians, or the Coccus 

 of the Greeks and Romans, but the scarlet grain of Poland, 

 and the still more valuable Cochenille of Mexico, together 

 with various kinds of bark-lice, agreeing with the former in 

 habits and structure. These insects vary very much in form; 

 some of them are oval and slightly convex scales, and others 

 have the shape of a muscle; some are quite convex, and either 

 formed like a boat turned bottom upwards, or are kidney-shaped, 

 or globular. They live mostly on the bark of the stems of 

 plants, some, however, are habitually found upon leaves, and 

 some on roots. In the early state, the head is completely 

 withdrawn beneath the shell of the body and concealed, the 

 beak or sucker seems to issue from the breast, and the legs are 

 very short and not visible from above. The females undergo 

 only a partial transformation, or rather scarcely any other 

 change than that of an increase in size, which, in some species 

 indeed, is enormous, compared with the previous condition of 

 the insect; but the males pass through a complete transforma- 

 tion before arriving at the perfect or winged state. In both 

 sexes we find threadlike or tapering antennae, longer than the 

 head, but much shorter than those of plant-lice, and feet con- 

 sisting of only one joint, terminated by a single claw. The 

 mature female retains the beak or sucker, but does not acquire 

 wings ; the male on the contrary has two wings, but the beak 

 disappears. In both there are two slender threads at the ex 

 tremity of the body, very short in some females, usually quite 

 28 



