The pupa of a Lepidopterous insect is completely encased in a chitinous envelope. With the exception of a slight twirling of the abdominal segments it is incapable of any motion. In the pupa of Micropteryx the mandibles and labial palpi are said to be functionally active, but this is a very exceptional though extremely interesting case. In conjunction with other evidence it would appear to indicate that the Lepidoptera originated from insects with active pupæ. The number of free or movable segments of pupæ varies considerably in different groups and genera, and by some modern authors it is regarded as a character of much importance in the framing of their classifications. The various organs of the perfect insect are distinctly marked out on the otherwise uniform integument of the pupa. In some groups, notably the Micropterygina, these organs are much more distinctly indicated than in others.
II.—ANATOMY.
THE PERFECT INSECT OR IMAGO.
In common with all other members of the class, the body of a Lepidopterous insect consists of three main divisions: (1) the head, (2) the thorax, and (3) the abdomen.
THE HEAD.
The front of the head is termed the face, the top the crown, the sides are nearly entirely occupied by the compound eyes (Plate [I]., fig. 11, AA), and the lower surface by the organs of the mouth.
The Eyes consist of a very large number of simple lenses arranged in the form of two hemispheres, one on each side of the head. The ocelli, or simple eyes, are situated on the crown, and are usually almost entirely covered by scales.
The Antennæ are two jointed appendages attached to the top of the head above the eyes. They vary very much in structure. The following are the terms used in describing the different forms of antennæ in the Lepidoptera:—
1. Pectinated, when the joints have long processes like the teeth of a comb. If these are on one side only, the antennæ are unipectinated; if on both sides, bipectinated. (Plate [I]., fig. 20, bipectinated antenna of Nyctemera annulata.)
2. Dentate, when the joints are armed with slight pointed spines.