Page:The Fauna of British India, including Ceylon and Burma (Butterflies Vol 1).djvu/12

viii Fig. 4.—Antennæ (apical portions much enlarged). a. Danais; b. Orsotriaœna; c. Hypolimnas; d. Pareba; e. Libythea; f. Abisara; g. Papilio; h. Pieris, j. Lampides; k. Tagiades.

For classificatory purposes the roost important parts are:—

Head (Fig. 2, I. & II.).—The labial palpi, b, b. These, in all butterflies, are three-jointed and variable in shape and in the clothing of scales or hair, but constant in each genus. They are independently moveable, but their function, if they have any, is unknown. The antennæ (e, e & II., also fig. 4) are evidently organs of perception. They are composed of an indefinite number of joints, and vary greatly in length and thickness, in the shape of the club, in the amount of scaling, and in the arrangement of the sensory hairs and pits. In very many forms they are grooved on the underside.

Thorax.—The appendages, the wings (figs. 5-10) and the legs (fig. 11), are of the utmost importance in classification.

Wings. These are membranous, traversed from the base outwards by nervures (“tubular structures which serve at once as extensions of the tracheal system and to form a stiff framework for the support of the wing”). In the vast majority of the butterflies they are covered on both upper and under sides with flat scales arranged in rows, and often brightly coloured. The usual number of nervures in the wings of butterflies are: fore wing 12; hind wing 9, beside the subcostal, median, and discocellular veins; but one or more of these may be absent, or there may be one or two extra veins or portions of veins developed.

Special note should be taken of fig. 5, as the details given explain the terminology used in the descriptions of the forms throughout this work. This terminology is different from that used in Moore's and de Nicéville's works. The following few additional terms will also be met with:— Anterior or upper and