{324}[Illustration: Fig. 165.—A, Section of male caterpillar of _Anosia plexippus_—muscular and tracheal systems and fat-body not shown: I, pro-, II, meso-, III, meta-thorax; 1-10, abdominal segments; _b_, supra-oesophageal ganglion; _c_, rectum; _d.v_, dorsal vessel; _g^3-g^9_, ganglia of ventral chain; _h_, head; _i_, intestine; _m.v_, Malpighian tube; _n.c_, nerve-cord of ventral chain; _oe_, oesophagus; _s_, spinneret; _s.o.g_, infra-oesophageal ganglion; _st_, stomach; _s.v_, silk-vessel; _t_, testis. B, One of the jointed prothoracic legs. C, An abdominal foot with its hooks. (After Scudder and Burgess, magnification about 2/1.)] There are three sets of glands opening by canals on the head, viz. the salivary glands proper, which open into the cavity of the mouth, one close to the base of each mandible; the silk-glands, which terminate by a common canal, continued externally as the spinneret; and the glands of Filippi situate in the head itself, and opening into the ducts of the silk-glands, near their union into a common duct. It should be recollected that Fig. 165 does not indicate all the details of the anatomy; the muscular system, for instance, being entirely omitted, though there are an enormous number of muscles; these however are not very complex, they being mostly repetitions in the successive segments.[185] The mouth-parts are very different from those of the perfect Insect, inasmuch as the maxillae and labial palpi, which are the most remarkable structures of the imago, are small, and are differently constructed in the caterpillar, while the mandibles, which are the largest organs of the caterpillar, disappear in the adult. The little organ by which the caterpillar exudes its silk is called a spinneret; according to Packard it is a "homologue of the hypopharynx." It is a more or less prominent point on the middle of the labium (Fig. 166, _g_) and sometimes forms a conspicuous spine projecting downwards. The eyes are extremely imperfect organs, consisting merely of six, in some cases {325}fewer, transparent, somewhat prominent, little spaces placed on each side of the lower part of the head; they are called "ocelli," by Landois "ocelli compositi." Under each of these external facets there are placed percipient structures, apparently very imperfect functionally, the caterpillar's sight being of the poorest character.[186] The spiracles of the caterpillar are nine on each side, placed one on the first thoracic segment and one on each of the first eight abdominal segments; there are no true stigmata on the second and third thoracic segments, though traces of their rudiments or vestiges are sometimes visible. [Illustration: Fig. 166—Front view of head of a caterpillar, with the jaws partially opened, _a_, Labrum; _b_, mandible; _c_, antenna; _d_, ocelli; _e_, maxilla; _f_, lingua; _g_, spinneret; _h_, labial palp.]