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 STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 411 



the metasternum. The posterior end of the metafurca bends 

 downwards and articulates with the posterior coxae on each 

 side. The metafurca serves for the attachment of the thoraco- 

 abdominal muscles. The pleural region of the metathorax is 

 a narrow triangular space situated behind the lateral portion 

 of the metasternum and the posterior coxae. It is composed 

 of a narrow triangular episternum and epiineron. The former 

 (eps."')is bounded in front by the metasternum^ the posterior 

 thoracic spiracle and the base of the haltere, below by the 

 posterior coxal foramen, and behind by the epimeron. The 

 epimeron (ep") is also bounded below by the coxal foramen and 

 behind by the narrow dorsal arch of the metathorax and the 

 first abdominal segment, its apex comes in contact with the 

 base of the haltere. The dorsal region of the metathorax has 

 practically disappeared, all that can be recognised as meta- 

 notum is a narrow chitinous strip (mn.) on each side between 

 the apex of the metapleural area and the dorsal edge of the 

 first abdominal area. 



Wings. The wings are situated at the sides of the 

 scutum on the alar membrane, to which are attached the 

 sclerites of the wing base. They are covered with very fine 

 hairs. 



In describing the neuration of the wings the nomenclature 

 proposed by Comstock and Needham (1898) for the wings of 

 the whole group of insects will be employed. 



The nervures of the wing are ocreacous. The anterior 

 edge of the wing (fig. 16) is formed by a stout nervure, the 

 costa ((/i.), which is very setose. The second longitudinal 

 nervure, the subcostal ($GI.), joins the costal about half way 

 along its length. A small transverse nervure, the humeral (h.), 

 divides the costal cell into costal (C.) and first costal (1 C.) cells. 

 The next main nervure the radial divides into a number 

 of branches (in the typical insect five) ; some of these have 

 coalesced in the fly. A nervure joining the costal just past 

 the middle is the first radial (B^) cutting off the subcostal 

 cell. The next nervure, which joins the costal on the apical 

 curve, represents the fused second and third radial nervures 



