The thorax is solidly put together, so as to bear the movements of the wings and legs. These latter are composed, as in other insects, of five parts: the coxa, the trochanter, the thigh, the shank, and the tarsus.
Many butterflies have all their six legs of equal length. In others, the two fore legs are very small, and are not suited for walking. In others, again, they are rudimentary, being deprived of hooks, very hairy, and applied on to the front of the breast.
| Fig. 135.—Leg of Butterfly armed with hooks. | Fig. 136.—Leg not suitable for walking. |
This difference of structure may be seen in Figs. [135] and [136], one of which represents, after Réaumur, a leg unsuited for walking, very hairy, and terminated in a sort of brush resembling the tail on a tippet; and the other a leg furnished with hooks.
The abdomen has the form of an elongated, or—in the majority of species—an almost cylindrical oval. It is composed of five segments, each formed of an upper and a lower ring, joined together by a membrane. The first are larger than the others, and generally overlap the edges, which gives to this part of the body the power of dilating considerably.
We must dwell longer on the head. It is generally rounded, compressed in front, longer than it is broad, and furnished with fine or scaly hairs. The important organs of which this part is the seat are the eyes, the antennæ, the palpi, and the proboscis or trunk.
The eyes are more or less spherical, surrounded by hairs, and composed of innumerable facettes. Colours are seen on these as various as those of the rainbow. But the colour which serves as a base to all, is black in some, grey in others; then again there are different gold or bronze colours of the greatest splendour, inclining sometimes to red, sometimes to yellow, sometimes to green. On the compound eye of a butterfly as many as 17,325 facettes have been counted. Simple eyes, or stemmata, are moreover observed in certain species, and are generally more or less hidden by scales.
The antennæ are situated near the upper rim or border of each eye. Réaumur has pointed out six principal shapes. One terminates in a little knob, and belongs to the butterflies. The others are variously shaped, and belong to the moths. Some are prismatic, or like beading. And lastly, others are shaped like feathers. We represent, in [Fig. 137], the different forms of the antennæ, which Réaumur collected together in plates 8 and 9 of his fifth Memoir. [46]
The palpi are four in number, two maxillary and two labial. The first are generally excessively small; one can only ascertain their existence by the aid of a strong magnifying glass: the second are in general very apparent, straight, cylindrical, covered with scales, and formed of three joints, of which the last is often very small and sometimes very pointed. They also sometimes bristle with stiff or silky hairs.