INSECTS. 



245 



rably adapted for grasping the round hair. Lice, however, are disagreeable 

 to contemplate, and we gladly leave them to take up other, if not more 

 pleasing, still more interesting forms. 



First of these are the so-called scale-insects, which are familiar to all as 

 small scales on the trunks of trees, on the leaves, or on the fruit. Tl 

 on the apple-tree are well known, and resemble somewhat the shell of an 

 oyster. These are the females, greatly changed in structure, and in real it v 

 forming but protective covers over the eggs and young. These scale- 

 insects occasionally do considerable injury, but some of them, on the other 

 hand, contribute to man's needs. One of these beneficial forms is the 

 lac-insect. This punctures the skin of the twigs of various East Indian 

 trees, and the exuding juice, drying on the exterior, forms the lac of 

 commerce, which, however, needs some treatment before it is 

 ready for the market. As broken from the tree it forms stick 

 lac. This is soaked in water to remove the coloring-matters, to 

 be mentioned farther on. It now has 

 a granular appearance, and is called 

 seed lac. The next process is to 

 melt it, after which it may either 

 be allowed to cool in large masses 

 (lump lac), or it is strained through 

 cloth and allowed to form a thin 

 layer on a flat board, where it soon 

 hardens and breaks up into small 

 scales, and is then the familiar shel- 

 lac, the most common form in trade. 

 It is used as the basis of an alco- 

 holic varnish, in sealing-wax, cements, and many other substances used 

 in the arts. 



The coloring-matter in the stick lac, to which allusion has just been 

 made, is composed of the bodies of the dead insects, and the bodies of the 

 females are colored a brilliant red. The aqueous extract referred to is 

 evaporated, and the residue, formed into lumps or cakes, forms the basis 

 of carmine lake, a pigment which rivals the carmine of the cochineal in 

 brightness and durability. The addition of various substances, like the 

 salts of alumina or tin, change the hue, and thus gives rise to quite a range 

 of red or reddish pigments. An allied species of insects living on the oaks 

 in the region around the Mediterranean affords the dye kermes, and these 

 two, it is supposed, were the basis of the rich crimson of the ancient- as 

 well as of the later red dyes of Holland and Belgium whose permanence is 

 so well known. 



■SUf" 



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Fig. 231. — Apple-bark covered with the scale-ins>«ts; 

 at the left, enlarged views of the young, the scale, 

 and the adult female. 



