STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 407 



mesotliorax. The protliorax and metatliorax compose very 

 small portions on the anterior and posterior faces respec- 

 tively. Seen from above the thorax is oviform with the 

 blunt end anterior and slightly flattened. Three transverse 

 sutures on the dorsal side mark the limits of the prescutum, 

 scutum, and scutellum of the mesothoracic segment; the 

 mesothoracic scutellum forms the pointed posterior end, and 

 slightly overhangs the anterior end of the abdomen. 



The Protliorax. — The prothoracic segment has been 

 reduced to such an extent that it is hopeless to attempt to 

 homologise all the separate sclerites with those of a typical 

 thoracic segment. To obtain a complete view of the pro- 

 thorax it is necessai-y to examine it from the anterior end 

 after the removal of the head. The following sclerites can 

 then be recognised. The presternum is a median ventral 

 plate, quadrilateral in shape having the anterior end rounded 

 and broader than the posterior end. It does not occupy the 

 whole of the prosternal area, but is bounded by the prosternal 

 membrane. Internally a ridge runs to the posterior end of 

 the presternum and bifurcates, each ridge running to the 

 posterior corners, to which two strong processes (the hypo- 

 tremata of Lowne) are attached. In front of the presternum 

 there is a small saddle-shaped sclerite which, on account of 

 its position, may be called the interclavicle (the sella of Lowne). 

 Two lobes at its anterior end are covered with small pro- 

 cesses, probably seusory in function. A pair of small sclerites 

 is situated in front of these lobes ; these sclerites with the 

 interclavicle no doubt belong to the prosternum. The inter- 

 clavicle is ventral to the cephalothoracic foramen. The 

 jugulares (3me jugulaires of Kunckel d'Herculais) are two 

 prominent pocket-shaped sclerites lying one on each side of 

 the cephalothoracic foramen, and having their convex faces 

 external. Lying immediately below each of the jugulares is 

 a small rod-like sclerite — the clavicle. The dorsal region of 

 the prothorax the pronotum (fig. 6 jjr.w.) is formed by two 

 sclerites united in the median line, their dorsal sides being 

 curved. From the ventral side of the pronotum a pair of 



