Bugs, Frog-hoppers, Scale Insects, &c. The structure of the mouth is the distinctive character of the insects of this great Order. Instead of the biting jaws (or sucking mouth) of many other insects previously described it is produced into a slender pointed tube of complicated structure, which usually lies along the under-surface of the head and thorax. This beak, called the rostrum, consists of a jointed sheath (labium) enclosing hair-like setae (mandibles and maxillae). When the insect feeds the sharp tip is pressed into its food, and the sap or juice sucked up, not by the proboscis-like sheath, but by the delicate enclosed setae. Kirkaldy doubts if the sheath “ever even penetrates the tissues, either vegetable or animal, unless these be already lacerated by the setae”; and it is often used only as a fulcrum to steady their operations. In the outward appearance (often a deceptive character in classification) the members of this group are very dissimilar; probably no two insects could be more unlike than the typical plant bug and the ordinary scale insect. They all undergo an incomplete metamorphosis, often changing their colours and even shape in the various moults before they are fully developed. The eggs of those living upon plants are generally deposited in clusters, and these are often very beautiful crystal spheres with stellate caps upon the summits. In other groups the eggs are buried in the tissue of the food plant or covered with woolly or sticky secretions. They take the name Hemiptera from the structure of the fore wing, one half of which is, in the typical bugs, horny and the rest semitransparent. The families of the plant and water bugs are much more closely related to each other than to the frog-hoppers, cicades and scale insects; and the whole Order has been separated into groups or sub-orders, viz., HETEROPTERA; HOMOPTERA; ANOPLURA; MALLOPHAGA. Sub-order I. HETEROPTERA. Bugs. This sub-division contains all the plant, carnivorous, and water bugs, which vary in size and shape from the tiny little leaf-infesting forms to the great “fish-killer,” _Belostoma indicum_, found in our water-holes. They are usually furnished with two pairs of wings. The basal portion of the front pair is horny and opaque, and the apical half more or less transparent; this pair covers the larger hind pair, which, well adapted for flight, are folded up beneath when at rest. The members of some groups however are apterous. Many are furnished with glands on the body secreting an offensive, buggy-smelling fluid, which they discharge when handled or disturbed.