(16) 



410 0. GORDON HEWITT. 



the episternum is intimately connected with the sclerites 1 of 

 the anterior portion of the wing-base. 



The epimeron (epS) is a triangular sclerite, and is bounded 

 below by the mesosternum and metasternum, behind by the 

 lateral plate of the postscutellum, and above by the episternum 

 and alar membrane. The "parapteron (pt.) is a sclerite situ- 

 ated at the top of the mesopleural membrane. The greater 

 portion of it is internal, only a small triangular portion can 

 be seen externally. Internally this is continued as a cruri- 

 form sclerite to which are attached important muscles con- 

 trolling the wings. The costa (ca.) is a small sclerite situated 

 on the dorsal margin of the epimeron. The internal skeleton 

 of the niesothorax consists of the eiitothorax, entopleura, 

 mesophragma, and the inflected edges of the episterna and 

 epimera. The entothorax is composed of a median vertical 

 plate subtriangular in shape, on the top of which a median 

 plate produced laterally into wing-like processes rests. On 

 this structure the thoracic nerve-centre lies. The entopleura 

 and the inflected edges of the episterna and epimera all serve 

 for the attachment of wing muscles. The mesophragma 

 (mph.) is a convex sclerite fused with the lower edge of the 

 postscutellum. Its posterior edge is incised in the middle 

 and forms the dorsal arch of the thoraco-abdonrinal foramen. 



The Metathorax. The largest sclerite of the greatly 

 reduced metathorax is the metasternum (mts.). It is a wing- 

 shaped sclerite with the narrow transverse portion situated 

 between the coxal foramina of the median and posterior pairs 

 of legs ; the expanded lateral portions form the wall of the 

 thorax above the insertions of these legs. The edges of the 

 narrow transverse strip are inflected, and unite the lateral 

 portions of the metasternum. A trough-shaped longitudinal 

 fold the metaf urea rests on the narrow transverse portion of 



1 In this account the individual sclerites which compose the wing base will 

 not be described. Lowne has described them at great length for the blowfly, 

 and although the wing-base sclerites ofM. domestica differ slightly in shape 

 from those of Calliphora, Lowne's description of their relations holds good 

 for the former insect. 



