The Structure of the Head and Mouth-parts in the Nycteribiidae (Diptera Pupipara)

Abstract

The investigation deals in detail with the structure of the immovable and movable parts of the head of the Nycteribiidae. The muscles of the head are also studied.The head capsule is modified from that of the Hippoboscidae. The vertex is not subdivided into several anatomically differing subregions. The occiput is represented by the border of the occipital foramen only. The postgenae are separated by the median membranous region of the head, as in the Hippoboscidae. The ptilinum serves as a flexible joint connecting the fronto-clypeus with the vertex and the genae. The fronto-clypeus is much more modified than that of the Hippoboscidae and is movable. The eyes are reduced to one or two facets, or are entirely absent. The greatly modified ocular sclerites are present in Cyclopodia only.The antennae consist of the pedicle and the flagellum, the latter being concealed in the cavity of the former. They have the same structure as those of the Hippoboscidae parasitising birds.The proboscis has much in common with that of the Hippoboscidae though it differs greatly in detail. It is composed of the rostrum, the haustellum and the labella.The rostrum belongs morphologically to the head and is formed of the same parts as in the Hippoboscidae. All the parts of the rostrum, with the exception of the tormae, have the same arrangement as in that family. The tormae are separate and are attached at the lateral borders of the fronto-clypeus.The haustellum is composed of the theca, the labial gutter, the labrumepipharynx and the hypopharynx. The two former parts belong morphologically to the labium, but differ in detail from those of the Hippoboscidae. The very short labrum-epipharynx is enclosed in the posterior part of the labial gutter.The hypopharynx is very slender and as long as the theca; it is enclosed in the cavity formed by the dorso-lateral parts of the labial gutter.Labial glands are present in the bulbous part of the theca; their ducts open into the food canal. All the muscles of the bulbous part of the haustellum are homologous with those of the same part of the proboscis of the Hippoboscidae.The labella are entirely membranous, are armed with two inner and six prestomal teeth and their surfaces have serrated ridges. There are six gustatory sensillae on the membrane of each labellum, which are connected by the intralabial canaliculi with the sense cells of the bulbous part of the theca.The cutting action of the teeth of the labella depends upon the protractions and retractions of the narrow part of the theca. When this part retracts it everts the inner membranous walls of the labella, and the teeth, being attached to these walls, perform protrusible divergent movements.