Like the butterflies, moths pass through the stages of egg, caterpillar, and chrysalis before they attain the perfect state (_imago_), and the duration of the several stages is just as variable. The majority assume the moth condition but once in the year, but some species have two, or even three, generations in the twelve months, whilst others occupy twenty-four months in completing the life cycle. In one or two species the chrysalis stage may last four, five, or even six years.
Diversity of form and structure is considerable in the early stages as well as in the perfect insects, and this is shown in the { 2} selection of life-history details figured on the black and white plates in this volume.
CONVOLVULUS HAWK-MOTH AND FLOWER OF NICOTIANA.
Except that it is generally less prominent, the head, with the various parts thereof, is pretty much the same as in the butterflies. In a few families, however, the "tongue" (proboscis) is only rudimentary or even entirely absent; while in others it is very long. The Convolvulus Hawk-moth has the proboscis of such length that it is able to reach the deep-seated nectary of such tubular flowers as those of _Nicotiana affinis_. In the illustration the "tongue" of the moth and the sweet-scented tobacco blossom are shown on exactly the same scale.
Fig. 2 represents some forms of antennæ found in moths. A, { 3} thickened and spreading out towards the tip (_dilate_); B, simple, thread-like (_filiform_) structure, without teeth, hairs, or bristles; C, fringed with fine hairs (_ciliate_); D, fringed with fine hairs, and with longer bristles at the joints (_setose ciliate_); E, the fringe in tufts (_fasciculate_); F, toothed, with fine hairs on the teeth (_dentate ciliate_); G, toothed with hairs in tufts from the teeth (_dentate fasciculate_); H, I, with double rows of hair scales (_bipectinate_); in I the projections are continued to the tip, and are themselves fringed with fine hairs, giving the antennæ a very feather-like appearance--the term "plumose" is sometimes used to describe this form of antennæ; in H the pectinations do not reach the apical fourth, which is simple. J, the _lamellate_, that is, the undersides of the rings or joints are made up of minute plates.