A decided advance toward a metamorphosis is exhibited by insects known as thrips (Fig. 4). Though readily overlooked on account of their minute size (one-twenty-fourth of an inch and less), they are nevertheless conspicuous on green foliage and white flowers owing to their blackish or yellowish colour. Thrips, when magnified, are easily recognised by their peculiar wings; each is feather-like, being formed of a narrow rib-like membrane clothed along the margins with long and delicate stiff hairs. Thrips’ eggs are laid upon the plant surface or within the tissues, according to the species, and are very minute (about one-twenty-third of an inch long). The larvæ puncture the plant tissues and feed upon the juices just as do the parents, which they resemble in general form, except that there are no wings and the antennæ are very short and the eyes small. There are two or three larval moults, after which the insect is more like the adult, though still resembling the larva. It now differs from the latter, however, in the antennæ being considerably shortened, and in the appearance of a pair of finger-like processes on each side of the body attached to the thorax and lying along the sides of the abdomen; these processes are the sheaths enclosing the wing rudiments of the future adult. The insect again moults, changing to a form resembling the preceding stage in many respects, but differing in the wing sheaths being much longer, and in having the antennæ, enclosed in sheaths of cuticle, turned back over the head. Although during these two stages the insect is capable of moving about, it is nevertheless sluggish and does not feed; from this second semi-quiescent stage the adult emerges. In the thrip’s cycle, therefore, although the habits of the larva and adult are similar, the presence of the two intermediate semi-quiescent stages, during which feeding ceases, shows a decided advance toward a true metamorphosis and represents a pupal stage. In the case of those insects not involved by a metamorphosis, as discussed above, the structure and habit of both adult and the immature stages differ but little, the development of wings being the principal change, except in the case of the thrips, where there is a definite tendency toward a pupa. However, passing on to a consideration of the common cicada (wrongly called a locust), a change in both structure and habit occurs during the life-cycle, the immature stages being adapted to a subterranean life, while the winged adult frequents the foliage of trees; all stages agree, however, in puncturing plant tissues with their proboscis and sucking up the nutrient juices from the roots by the larva and from the stems and leaves by the adult.