LABYRINTH ORGAN: see EQUILIBRIUM, ANIMAL.
a resinous incrustation formed on the twigs and young branches of trees by an insect, Coccus lacca, which infests them. The term lac is the same as the numeral lakh—a hundred thousand —and is indicative of the countless hosts of the insect. Lac is a product of the East Indies, especially Bengal, Pegu, Siam and Assam, and is produced on a number of trees, particularly Ficus religiosa. The insect which yields it is closely allied to the coch ineal insect, C. cacti; kermes, C. Rids; and Polish grains, C. Polonicus, all of which, like the lac insect, yield a red colouring matter. The minute larvae fasten in myriads on the young shoots, and, inserting their long proboscides into the bark, draw their nutriment from the sap. The insects exude the resinous secretion over their entire bodies; this forms in effect a cocoon, and, the separate exudations coalescing, a continuous, hard, resinous layer honeycombed with small cavities is deposited over the twig. From this the females, which form the bulk, never escape. After im pregnation, which takes place on the liberation of the males, about three months from their first appearance, each female develops into an amorphous organism consisting in its main features of a large, smooth, shining crimson sac—the ovary—with a beak stuck into the bark, and a few papillary processes above the resinous surface. The red fluid in the ovary forms the lac dye of com
merce. To obtain the largest amount of both resin and dye the twigs with their living inhabitants must be gathered in June and November. Lac as gathered is known as "stick lac"; the resin, crushed to small fragments, washed in hot water to free it from colouring matter, melted, strained through thick canvas, and spread out into thin layers, is "shellac," and is the form in which it is usually brought to European markets. Shellac varies in colour from dark amber to almost black ; the palest, "orange-lac," is the most valuable. Shellac may be bleached, the product being known as white shellac. Bleached lac takes delicate shades of colour, and dyed yellow it is used in the East Indies for ornaments. Lac is a principal ingredient in sealing-wax, and forms the basis of valuable varnishes, besides being useful in cements, etc.