STOMOXYS CALCITRANS 



835 



in so doing is suspected of spreading trypanosomes, especially 

 r. evansi. Manders considered S. nigra Macquart, 1850, to be the 

 cause of the spread of surra in Mauritius. 



It is rather like the common house-fly, but is easily recognized 

 by the head being raised in the resting position, by the projecting 

 proboscis, and by the closed wings, touching one another at their 

 bases, and diverging behind. 



Fig. /[2j .-—Stomoxys calcitrans : Female. 



Morphology. — The mouth-parts consist of a proboscis, composed of rostrum, 

 haustellum, and labellse, which are bent posteriorly, forming an elbow-shaped 

 joint. The posterior portion can be retracted or projected forwards, and 

 carries the chitinous fulcrum of the pharyngeal wall, the maxillae, and their 

 palps. It is cone-shaped, and is called the rostrum. 



The structure of the haustellum, or proboscis proper, is very complex. It 

 consists essentially of a labrum, hypopharynx, and labium. The labrum is a 

 sharp-pointed stylet, which near its apex bears a ventral ridge with four 

 sensory hairs. Posteriorly it is attached to the head, where it forms a chitinous 

 projection. It is horseshoe-shaped on transverse section, the ventral opening 

 being closed by the hypopharynx, while laterally its walls, which expand and 

 enclose a cavity containing muscles, articulate with the labium, thus keeping 

 the hypopharynx in its place. The hypopharynx, which contains the salivary 

 tube, starts from the labium and runs forwards, expanding laterally and 

 closing in the labial, pharyngeal, or blood-tube mentioned above. Its lateral 

 expansions contain a cavity. At its tip it appears to be membranous, which 

 ^ Stephens and Newstead think by its flaccid condition prevents ingress of fluid 

 during blood-sucking, while freely permitting the egress of saliva. The 

 labium is stout and thick, with a swollen basal portion, gradually tapering 

 towards the proximal and distal extremities, but less so basally. Posteriorly 

 it encloses the labrum and hypopharynx, which it carries on a sclerite, which 

 farther forwards forms the boundary of the labial gutter, and is joined dorsally 

 by another dorsal hooked sclerite. These sclerites stop at the base of the 

 labellge. Ventral to the dorsal sclerites are two ventral sclerites, which 



