The structure and function of the mouth-parts, rostrum and fore-gut of the Weevil Calandra granaria L

Abstract

The mouth-parts of Calandra granaria are situated at the tip of an elongated rostrum. The mandibles are asymmetrical and possess a markedly oblique axis of rotation which determines the precise mode of action of their teeth. Extremely long bracons attached near their molar regions lie in the lumen of the pharynx. The maxillae although considerably specialized still show to a large extent their constituent parts. They lie in an almost vertical plane against the lateral walls of the labium, and are chiefly concerned with the transport of food from the mandibles to the mouth opening. The mechanics of the movements of the maxillae are discussed. No indication of the areas involved in the rigid labium is afforded by the presence of sutures. A dorsal ligula is present, and between the ligula and the main body of the labium a pair of labial palps is revealed by sectioning. A backward extension of the labial roof is fused to the floor of the pharynx and gives it support. The muscles of the mouth-parts lie completely within the head capsule, and operate the mouthparts through the intervention of long tendons. These tendons are supported and guided in the rostrum by apodemes. The pharynx consists of a long trough with a thin roof. Only the roof is provided with muscles, capable of elevating and depressing it. A median tract of spines in the roof operates in conjunction with the pharyngeal bracons in the transport of food along the pharynx. The stomatogastric nervous system, consisting of paired frontal ganglion connectives and labral nerves, and a median recurrent nerve, is described. The median frontal ganglion of the generalized nervous system is replaced by small paired lateral frontal and labral ganglia and a simple median plexus. True maxillary glands, opening near the bases of the maxillae, are present. The structure and function of the oesophagus, crop and proventriculus are described. The proventriculus functions as a sieve retaining food in the crop until partially digested.