Fig. 31.—Head of Limnephilus pudicus, under side: e, eye; l, ligula; p, palpifer; lp, labial palpi.
The occiput (Fig. 29, B, C), as stated beyond, is very rarely present as a separate piece; in the adult insect we have only observed it in Corydalus. The occipital region may be designated as that part of the head adjoining and containing the occipital foramen. Newport considers the occiput as that portion of the base of the head “which is articulated with the anterior margin of the prothorax. It is perforated by a large foramen, through which the organs of the head are connected with those of the trunk. It is very distinct in Hydroüs and most Coleoptera, and in some, the Staphylinidæ, Carabidæ, and Silphidæ is constricted and extended backwards so as to form a complete neck.” (See also p. 51.)
Fig. 32.—Interior and upper and under surface of the head of Hydroüs piceus: d, clypeus; e, labrum; g, maxilla; h, its palpus; i, labium; k, labial palpus; p, sutura epicranii; q, cotyloid cavity; r, torulus; s, v, laminæ squamosa; t, laminaæ posteriores; u, tentorium; w, laminæ orbitales; x, os transversum; y, articulating cavity for the mandible; z, os hypopharyngeum.—After Newport.
The tentorium.—The walls of the head are supported or braced within by two beams or endosternites passing inwards, and forming a solid chitinous process or loop which extends in the cockroach downwards and forwards from the lower edge of the occipital foramen. “In front it gives off two long crura or props, which pass to the ginglymus, and are reflected thence upon the inner surface of the clypeus, ascending as high as the antennary socket, round which they form a kind of rim.” (Miall and Denny.) The œsophagus passes upwards between its anterior crura, the long flexor of the mandible lies on each side of the central plate; the supraœsophageal ganglion rests on the plate above, and the subœsophageal ganglion lies below it, the nerve cords which unite the two passing through the circular aperture. (Miall and Denny.) In Coleoptera (Hydroüs) it protects the nervous cord which passes under it. (Newport, Fig. 32, u.)
Fig. 33.—Posterior view of head of Anabrus; t, tentorium. Joutel del.
In Anabrus the tentorium is V-shaped, the two arms originating on each side of the base of the clypeus next to the base of each mandible the origin being indicated by two small foramina partly concealed externally and passing inwards and backwards and uniting just before reaching the posterior edge of the large occipital foramen (Fig. 33).
Palmén regards the tentorium as representing a pair of tracheæ (with the cephalic spiracles) which have become modified for supports or for muscular attachment, since he finds that in Ephemera the tentorium breaks across the middle during exuviation, each half being drawn out of the head like the chitinous lining of a tracheal tube. This view is supported by Wheeler, who has shown that the tentorium of Doryphora originates from five pairs of invaginations of the longitudinal commissures, and which are anterior to those of the second maxillary segment. “These invaginations grow inwards as slender tubes, which anastomose in some places. Their lumina are ultimately filled with chitin.” (Jour. Morph., iii, p. 368.)