In passing in review the various insects the peculiar transformations through which they pass are noticed; some long, some short, some partial, and many complete. In the cicada, or seventeen-year locust, or harvest fly, we have an instance of one of the strangest examples of slow development known. The cicada is a wedge-shaped insect having some resemblance to a huge fly. At the base of the abdomen is a drumlike organ by which it makes a shrill "zeeing" sound which, when thousands are joined in concert, produces a remarkable sound audible for a long distance. I have heard it half a mile with the wind, and by following it up found a grove filled with insects producing a roar of sounds, while, clinging to the trees and branches, were thousands of empty skins from which the cicadas had escaped. The cicada deposits three or four hundred eggs in holes on the twigs or bark of the oak. They hatch very promptly in six weeks or so, and we might conclude that the young cicadas would soon appear. But seventeen long years of life underground are now required before the pupa crawls upward, molts, and appears as an adult cicada. It has spent all these years as an almost helpless creature, resembling the mole cricket, subsisting by sucking the juices from the roots of plants, waiting for the ending of its imprisonment. [Illustration: FIG. 213.--Halobates, a bug that goes to sea.] [Illustration: FIG. 214.--Young leaf hopper and its bubbles.] On many plants the stroller through the garden will observe bits of white froth, like soap suds, and few persons, were they not in the secret, would believe that the froth is an especially devised medium for the little leaf hopper (Fig. 214). The adult insect is a curious little creature found among the grasses in spring. The young require moisture to enable them to attain their full development, and when hatched they climb up stalks of grass and pierce them with their beaklike proboscis and gorge themselves with the juices. The insect now exudes a foamy secretion which bubbles up about it, in time entirely surrounding itself in a mass of moisture. The insect converts this into air globules by pushing its tail above the mass (_a_) and seizing air in its claspers, which it passes beneath it to the spiracle or breathing pore. In this way it breathes and also fills the section about it with air. There the animal passes the time until it is ready to change, when it escapes and becomes a perfect leaf hopper. The famous cochineal insects (Fig. 215) belong to this group. They are minute creatures which live upon certain cacti in the tropics. When collected they form the celebrated dye. Another form produces a valuable wax. [Illustration: FIG. 215.--Cochineal insect.]