This order includes the Butterflies and Moths, they have four wings, which are large and covered with minute scales, which are for the most part of a heart or battledore shape, as in fig. 27. The wings of these insects are many of them beautifully marked and tinged. There are about 12,000 species, by some divided into "diurnal" (or those which fly by day), "crepuscular" (or those which fly in the evening), and "nocturnal" (or those flying by night). The Moths are mostly crepuscular and nocturnal, while the Butterflies are chiefly diurnal, but the most usual distinction between the Moth and Butterfly consists in the form of the antennæ, those of the Moth being feather-shaped, while those of the Butterfly have a small knob at the end, or, as it is called, "club-shaped." The Lepidoptera feed upon the nectar of flowers, for which purpose they are furnished with a long proboscis or "Haustellium," which is curled up under the head, it consists of two semi-cylindrical pieces which when placed side by side form a tube, up which the nectar is drawn by capillary attraction. The metamorphosis of these insects is complete. The Silkworm (Bombyx mori) belongs to this order. It is the most important of all insects to man, as from it alone all the silk of commerce is obtained. Its cocoon is of a beautiful yellow colour, varying in shade from orange to pale straw-colour; the silk of one cocoon weighs somewhere about three grains; it would therefore, at this calculation, take 1920 worms to spin one pound. The annual import of silk into this country alone is about 7,000,000 pounds, it must therefore take 13,440,000,000 Silkworms to supply us with silk yearly! The Silkworm feeds almost exclusively on the leaves of the mulberry. [Illustration: FIG. 28.--THE SILKWORM (Bombyx mori). 1, the Eggs; 2, the young Silkworms; 3, the full-grown Silkworm; 4, the Cocoon; 5, the Chrysalis; 6, the Moth.] 7. HEMIPTERA (Half-winged). The Hemiptera have two pairs of wings, the hindermost small, and the foremost pair half horny and half membraneous, the base being horny, and the apex membraneous. They include the Bugs, some of which are aquatic, as the Water Scorpion (Nepa), and the Water Boatman (Natonecta), which swims on its back, rowing itself by means of a pair of long legs, which look like oars; the common bed Bug is also of this order, although wingless, as are also the Plant Lice (Aphides), which, however, obtain wings in their perfect state. 8. DIPTERA (Two-winged). [Illustration: FIG. 29.--PART OF GNAT'S WING, MAGNIFIED. ]