The chief feature in the anatomy of the larva is the great size of the stomach. There is a very short oesophagus and crop; the latter becomes enlarged, spreading out so as to form the stomach, a great sac occupying the larger part of the body-cavity (Fig. 165). On the hinder end of this sac the Malpighian tubes open; they are similar in their disposition to those of the imago; behind the stomach the canal expands into two successive, short dilatations, the first called an intestine, the second a rectum; they are connected by very short isthmuses. The dorsal vessel is a simple, slender tube, extending from the eighth abdominal segment to the head. The main nervous system consists of supra- and infra-oesophageal ganglia, a small frontal ganglion, and a ventral chain of eleven ganglia, three thoracic and eight abdominal, the last of these latter being double. The sexual organs are quite rudimentary, and the passages connected with them very incompletely developed. PUPA.—The pupa, which is one of the most remarkable of the instars of an Insect's life, attains its highest development in Lepidoptera. The Lepidopterous pupa is frequently called a "chrysalis," a term originally applied to certain metallic butterfly pupae. The Lepidopterous pupa differs from that of other Insects in the fact that its outer skin forms a hard shell, all the appendages of {327}the body being glued together by an exudation so as to form a single continuous outer skin. This form of perfect pupa is called "pupa obtecta." The obtected pupa is exhibited in various stages of perfection in the Lepidoptera; the maximum of perfection is attained by the pupae of such butterflies as are exposed without protection or concealment; on the other hand, we find in various small moths conditions of the pupa that do not differ in any marked manner from the pupae of Insects of other Orders. Moreover, certain Coleoptera and Diptera exhibit obtected pupae of a more or less perfect kind. Hence the pupa obtecta is to be considered as a perfected condition that exists more frequently in the Lepidoptera than in other Orders. [Illustration: Fig. 167.—Section of female pupa of _Anosia plexippus_, 3-4 days old. I, pro-, II, meso-, III, meta-thorax; 1-9, abdominal segments; _a_, antenna(?); _ac_, aortal chamber; _ag^1-ag^5_, abdominal ganglia; _agl_, accessory glands; _ao_, aorta; _br_, brain; _c_, colon; _cp_, bursa copulatrix; _cr_, cremaster; _f^1_, first femur; _fr_, food-reservoir; _h_, dorsal vessel; _i_, part of intestine; _mv_, Malpighian tube; _mx_, base of maxilla; _oe_, oesophagus; _ov_, ovary; _ph_, pharynx; _sd_, salivary duct; _sgl_, salivary gland; _st_, stomach; _t^1_ first tarsus; _tg_, compound thoracic ganglion; _ts^2_, _ts^3_, second and third tarsus. (After Scudder.)]