The silverfish (Fig. 4), wingless throughout life, measures about one-quarter of an inch long when full grown; it is silver-white in colour, due to a clothing of glistening scales that rub off as a silky powder when the insect is handled. It glides rapidly about, especially after dark, and is one of the most primitive insects, there being minute leg-like processes attached in pairs to the under side of the abdomen; the normal thoracic legs are well developed. The body is wedge-shaped, tapering to the posterior end, from which three tail-like appendages project, while anteriorly a pair of long, delicate antennæ arises from the head. All stages of the silverfish, from the minute, freshly-hatched individuals to fully-grown ones, may be found in the one place, the smaller ones being immature developing stages. In the case of another species allied to the common silverfish, the female lays from six to ten eggs at one time in sheltered crevices, and the young hatch forty-five to sixty days later, when the temperature ranges from 65 degrees to 68 degrees Fahrenheit. Unlike the moth larva, that of the silverfish throughout its growth resembles the adult both in habit and form, the only marked differences being that of size and the absence of the abdominal leg-like appendages. During growth several moults take place, and at the final one the adult appears with all its characteristics. Some species take two years to reach maturity. In this type of insect there is, therefore, no pupal or resting stage, and the larval habits and food are the same as those of the adult insect, while there is but little difference in structure throughout all the stages. There are many winged insects (_e.g._, cockroaches, crickets and earwigs) that show a slight advance toward a metamorphosis. Though their larvæ differ from the adults principally in the absence of wings, there are stages between the younger larvæ and the adults in which the wing rudiments appear. These rudiments first appear after one of the moults as small bud-like structures on each side of the thorax (earwig, Fig. 4), becoming larger after each succeeding moult, when the developing wings may be seen enclosed in a sheath of the cuticle; at the final moult the wings, no longer enclosed in their coverings, straighten out and become functional. A very pronounced difference is here noted between the wing development of such insects and that of a moth, in that the wing rudiments of the former develop externally and those of the latter internally.