The Anatomy of the Head and Mouth-parts of Dysdercus intermedius Dist.



Miss H. Frazer has given a brief general account of the mouth-parts of Dysdercus intermedins in her paper on the transmission of internal boll disease of cotton. In the present paper this description is amplified and augmented.

The arrangement of the sclerites forming the head capsule of D. intermedius is described. The maxillary plates have internal projections, the maxillary processes, which support the stylets in the anterior part of the head.

The sucking pump, described as the pharynx by many authors, is an external chamber and not a true pharynx. It is formed by the flexible dorsal epipharynx, to which are attached the dilator muscles, and the rigid, ventral hypopharynx. The anterior end of the hypopharynx is drawn out into the pharyngeal duct which is inserted into the suction canal between the stylets.

The two pairs of stylets are enclosed in a chamber, the stylet pouch, formed inside the head by the invagination of the outer wall of the head capsule and by the wing of the hypopharynx. The mandible is the outer of the two stylets. The protractor muscle of the mandible is attached to the mandibular lever and not directly to the stylet; the retractor muscle is directly attached to the base of the mandible. The maxillary stylet represents the lacinia of the maxilla of other insects, the rest of the appendage forms the maxillary plate. Both the pro- and retractor muscles of the maxilla are attached to the base of the stylet. There are no maxillo-mandibular muscles.

The saliva is forced down the salivary canal between the stylets by a highly developed salivary syringe. Two salivary ducts, their openings guarded by simple valves, open into the pump chamber. There is no valve at the exit of the common ejaculatory duct which runs through the body of the hypopharynx and opens into the salivary canal between the stylets.

The epipharynx is pierced by two series of pores leading to sensory cells lying dorsal to the epipharynx. Prom their position these cells are supposed to be a gustatory organ.

Dysdercus intermedius has paired maxillary glands lying inside the maxillary plates and opening by numerous small pores on their anterior faces. It is suggested that the secretion from these glands may be to lubricate the stylets or to help to bind the stylet bundle together and so strengthen it.

The salivary glands are of the four-lobed type with duct-like accessory glands.