and that prognathism in insects to-day is a secondary condition. As Macropathus filifer exhibits a number of primitive characters it seems that Snodgrass's statement is probably more correct.

Antennae Figs. 3, 4. Situated on the inner side of and partially below the compound eyes; the long, slender, tapering, very flexible sensory flagella are four and a-half times as long as the body in both male and female (excluding ovipositor in females). The antennal sclerite (Asl) forms a ring at the base of each antenna, which is separated from the rest of the head-capsule by the antennal suture (As). The scape (S) of each antenna articulates with a lateral process on the antennal sclerite and is connected all round to the antennal sclerite by a membrane (Im). In the male (Fig. 3, A, B), the scape is greatly enlarged, about four times the size of the pedicel (P) which, although narrower and shorter than the scape, is broader than the other segments. The third segment, on the dorsal aspect, is narrower, but half as long again as the pedicel, and on the ventral aspect equals the pedicel in length. From the fourth segment onwards the segments are unequal in length, although steadily decreasing in size. Some segments are only partly divided; some have a ventral retrolateral spine (Sp) in which case the distal part of the segment is swollen and the spine is borne on this swelling; prolateral spines entirely absent. This spination of the antennae is found only in the mature male, and there is great variability in the number of spines present (Fig. 3, C); it is an example of sexual dimorphism. In the female (Fig. 4, A, B, C) the antennae are essentially the same except that the scape is not as thick as that of the male and consequently the flagellum is not as long. In both sexes the antennae are thickly clothed with setae. The long flagellum is easily broken so that the length varies, and in no cases has regeneration of lost segments been observed after an ecdysis.

Compound Eyes And Ocelli. Two pear-shaped compound eyes (Fig. 1, Ce) lie dorso-laterally to the antennae. Between the antero-medial margins of the antennal sclerites on the frons (Fig. 1, Fr) is a small white pear-shaped structure which is the only ocellus (Fig. 1, Oc) that survives in Macropathus filifer. Each eye, in which there are approximately a thousand facets, is surrounded by a chitinous ring, the ocular sclerite (Fig. 2, Osl), and where it joins the head-capsule is the ocular suture (Figs. 1, 2, Ocs). There is a small white area in the dorso-posterior region of each eye where the facets of the eye are much smaller.

Capsule Figs. 1, 2, 5 The frons (Fr) is the median sclerite lying directly anterior to the epicranium (Ep), but not separated from it by a suture. Laterally there is no fronto-genal suture to divide it off from the gena; distally it is separated from the clypeus (C) by the invaginations forming the anterior arms of the tentorium, but the greater part of the clypeus is continuous with the frons and the epistomal suture is absent. The clypeus is divided ventrally into ante-clypeus (C) and dorsally into post-clypeus (Pc) by the clypeal suture (Cf.). At the junction of the post-clypeus with the mandibular sclerite (Mns) is a concave process that articulates with the ginglymus (Gl) of the mandible The post-clypeus is brown and chitinized and the ante-clypeus is white and membranous. The cheek is formed by the gena which is separated from the mandibular sclerite by the subgenal suture (Sgs); postero-laterally it is separated from the narrow postgena (Pg) by the occipital suture (Os); dorso-laterally it is separated from the vertex (V) by another suture unlike anything found