The antennae consist of eleven to twenty-five joints, or even more, about thirteen being the usual number; the basal two are thicker than the others, and are destitute of setae or pubescence such as the others possess. The maxillae and labium are remarkable. The former possesses a peculiar hard pick or elongate rod; this is considered by many naturalists to be the inner lobe, but Burgess thinks it more probably an independent organ,[307] as it has no articulation of any kind with the outer lobe. The latter is remarkably thick and fleshy; the palpus is 5-jointed. Other authorities consider the pick to be certainly the inner lobe; if it be not, the latter is quite wanting. Hagen agrees with Burgess in stating that the pick slides in the outer lobe as in a sheath. The labium has a large mentum and a ligula divided anteriorly into two lobes; at each outer angle in front there is a globular projection, which is doubtless the labial palpus; reposing on the labium there is a large free lingua. The labrum is large, attached to a distinct clypeus, behind which there is a remarkable post-clypeus, which is usually prominent as if inflated; to its inner face are attached several muscles which converge to be inserted on a plate placed below the anterior part of the oesophagus, and called by Burgess the {392}oesophageal bone; under or within the lingua there is a pair of lingual glands. Judging from Grosse's study of the mouth of Mallophaga, we may conclude that the oesophageal bone will prove to be a sclerite of the hypopharynx. The eyes of the winged forms are frequently remarkably convex, and there are also three ocelli, triangularly placed on the vertex. The head is free and very mobile. The coxae are rather small, exserted, contiguous; the sterna small. The abdomen has usually ten segments, though sometimes only nine can be detected. The thorax in Psocidae usually looks as if it consisted of only two segments. This is due to two opposite conditions: (1) that in the winged forms the prothorax is reduced to a plate concealed in the fissure between the head and the mesothorax bearing the first pair of wings; (2) that in the wingless forms (Fig. 247), though the prothorax is distinct, the meso- and metathorax are fused into one segment. [Illustration: FIG. 244.—Reproductive organs of _Clothilla pulsatoria_. A, Male; _a_, vesiculae seminales; _b_, testes; _c_, vasa deferentia; _d_, ejaculatory duct. B, Female; _a_, _b_, egg-tubes; _c_, oviduct; _d_, uterus, containing egg; _e_, accessory gland (the enveloping sac in section); _f_, its duct. (After Nitzsch.)]