Fig. 215.—Under-surface of head of Lipeurus heterographus. (After Grosse.) ol, Labium; md, mandible; mx, maxilla; ul, labium.
Fig. 216.—Under lip of Nirmus, A; and of Tetrophthalmus chilensis, B. (After Grosse.) m, Mentum; g, ligula; pl, palp; pg, paraglossa; hy, lingua.
The eyes are very rudimentary, and consist of only a small number of isolated facets placed behind the antennae; sometimes they are completely absent. The mouth parts are situated entirely on the under-surface of the head and in a cavity. The upper lip is frequently of remarkable form, as if it were a scraping instrument (ol, Fig. 215). The mandibles are sharply toothed and apparently act as cutting instruments. The maxillae have been described in the principal work on the family[[270]] as possessing in some cases well-developed palpi. According to Grosse[[271]] this is erroneous; the maxillae, he says, are always destitute of palpi, and are of peculiar form, being each merely a lobe of somewhat conical shape, furnished on one aspect with hooks or setae. The under lip is peculiar, and apparently of very different form in the two chief groups of Mallophaga. The large mentum bears, in Liotheides (Fig. 216, B), on each side a four-jointed palpus, the pair of palps being very widely separated; the ligula is broad and undivided; on each side there is a paraglossa bearing an oval process, and above this is a projection of the hypopharynx. In Philopterides (Fig. 216, A) the palpi are absent, and the parts of the lower lip are—with the exception of the paraglossae—but little differentiated. The lingua (hypo-pharynx) in Mallophaga is largely developed, and bears near the front a chitinous sclerite corresponding with another placed in the epipharynx.
The prothorax in Mallophaga is a distinct division of the body even when the meso- and meta-thorax appear to be part of the abdomen. The mesothorax is frequently very small; it and the metathorax are sometimes intimately connected. In other cases (Laemobothrium) the metathorax appears to differ from the following abdominal segment only by having the third pair of legs attached to it. In Trinoton (Fig. 214) the three thoracic segments are well developed and distinct. The abdominal segments visible, vary in number from eight to ten; there is sometimes a difference according to sex, the male having one segment taken into the interior in connexion with the reproductive organs. The legs have short, broad coxae and small tarsi of one or two joints; very rarely three joints are present; there are either one or two claws; the legs with one claw being adapted for clinging to or clutching hairs. The front pair of legs is used not for locomotion so much as for grasping the food and bringing it within the range of the mouth. No trace of wings has been detected in any species.
Fig. 217.—Ganglia of nervous system of Lipeurus bacillus. (After Giebel.) a, Cavity of head.
The nervous system has been examined by Giebel in Lipeurus bacillus; there is a supra- and an infra-oesophageal ganglion, and three thoracic, but no abdominal ganglia. The supra-oesophageal is remarkably small, in fact not larger than the infra-oesophageal; it consists evidently of two conjoined halves. The alimentary canal has a slender, elongate oesophagus, dilated behind into a crop; this is frequently received between two cornua formed by the anterior part of the stomach, which, except for these, is simply tubular in form, though somewhat narrower at the posterior extremity. In some forms—Philopterides—the crop is of a very peculiar nature (Fig. 218), forming an abrupt paunch separated from the stomach by the posterior portion of the oesophagus. There are only four Malpighian tubes; in some species the basal half of each tube is much dilated. The two divisions of the intestine are short and are separated by the intervention of a glandular girdle. Salivary glands exist; Giebel figures what we may consider to be an enormous salivary reservoir as existing in Menopon leucostomum.
The testes and ovaries are of a simple nature. The former consist of two or three capsules, each having a terminal thread; the vasa deferentia are tortuous and of variable length; they lead into the anterior part of the ejaculatory duct, where also opens the elongate duct proceeding from the bicapsular vesicula seminalis; these structures have been figured by Grosse[[272]] as well as by Giebel. The ovaries consist of three to five short egg-tubes on each side; the two oviducts combine to form a short common duct with which there is connected a receptaculum seminis.