The first principal character separating the Coccididæ from the rest of the Homoptera, and distinguishable without microscopic examination, is the absence of wings in the females at all stages of their existence. The second principal character is the absence of any apparatus for feeding and digesting in the males. From these two characters it follows that the females can only extend their operations by, at the best, crawling from plant to plant, or by being carried about by birds or other agency; also that the males cannot enjoy more than a very short existence, their work being entirely confined to impregnating the females. Hence, in any endeavours to destroy these insects, the males may be disregarded, and the females only attended to. Other distinguishing characters, chiefly microscopic, are-- 1. The presence of only one joint in the tarsus or fourth joint of the leg, in both males and females (Plate i., Figs. 6 and 7, _ta_); 2. The presence of only a single claw terminating the leg in both males and females (Plate i., Figs. 6 and 7); 3. The presence of only two wings, with two halteres, in the full-grown males (Plate xxi.); 4. The presence of two or more eyes or ocular tubercles, in addition to the ordinary pair of eyes, in the full-grown males (Plate i., Fig. 14; Plate viii., Fig. 1, _k_, _m_). I. The Female Insect. In general outward appearance the female insects present very variable forms. They may be either naked, or covered over with some kind of a shield, which may be fibrous, or waxy, or cottony, or they may have simply a thin powdery meal scattered over them. The covered insects are, of course, stationary, although in some cases, before reaching their full development, they move about, carrying their houses with them. The naked insects may be either stationary or active. They attach themselves either to the bark or stem of a plant or to the leaves. In the latter case it is rare to find them on the upper side; but, on turning over a leaf, the under-surface is frequently found covered thickly with them. In many cases they exude, in the form of minute globules, a whitish, thick, gummy secretion, answering probably to the "honeydew" of the Aphididæ. This secretion drops from them on to the plant, and from it grows a black fungus, which soon gives an unsightly appearance to the plant. This fungus or "smut" is an almost invariable indication that a plant is attacked by insects,[C] and may, indeed, give a useful warning to tree-growers. It is not, however, produced in appreciable quantities by all species. [C] Not necessarily a Coccid insect: the fungus may also grow on the honeydew of Aphis; but it is easy to recognize the difference between these insects. In every case there is some insect at work where the fungus is.