374 KANSAS UNIVERSITY SCIENCE BULLETIN. 



THE THORAX OF SIMULIUM. 



The thorax of dipterous insects always presents a problem. 

 The fact that they possess but one pair of wings has led to the 

 adjusting of the thoiacic box to meet these conditions. Thus 

 the mesothoracic division which bears the wings is greatly de- 

 veloped while the prothoracic and metathoracic divisions are 

 reduced. Time has not permitted a detailed leport on the 

 homologies of the several sclerites making up the prothorax. 

 Suffice it to say that the prothoracic cylinder is not typical, the 

 sclerites conforming not at all to our conception of the norma! 

 arrangement of parts. The mesothoiax, on the other hand, is 

 a simpler matter. The notum is large, occupying the whole 

 of the dorsal side of the thorax. It is not transversed by well- 

 marked sutures that could mark the prsescutum, scutum, scu- 

 tellum, and po.stscutellum. As a whole it is a convex shield. 

 It is this sclerite that gives to Simulium its characteristic 

 "humpedback" shape. 



Laterally, we have the alar membrane for the wing attach- 

 ment above and the episternum and epimeron below. The 

 mesosternum is large and well marked. The metathorax bears 

 the haltere and the metathoracic spiracle on its pleural aspects. 



Wings. The two wings are borne at the sides of the scutum 

 of the mesothorax. They are attached, by means of the 

 sclerites at the base of the wings, to the alar membrane. They 

 are broad and characterized by having only the veins of the 

 anterior portion of the wing developed, the other veins show- 

 ing only as thickened but transparent tracings. (See Fig. 1, 

 PI. XLIII.) Following the nomenclature of Johannsen for 

 this family I describe the venation of the wing as follows : 

 The anterior edge of the wing is reenforced by the costa which 

 extends to a point some little distance before the tip of the 

 wing. The siibcosta joins the costa at a point about one-third 

 the distance from the base of the wing to the tip. Radius is 

 all but fused with fnibcosta, showing up a clear line along the 

 posterior edge of subcosta for ''5 of its length, (subcosta), 

 it then appears as a separate vein. R. joins costa a little be- 

 yond the point where subcosta meets costa. This' point is 

 marked by a slight emargination in the costal margin of the 

 wing. R2-3-Jf-5 extends for a considerable distance, finally 

 meeting costa shortly before its termination (costa). The 

 base of media is well marked. This well-marked portion ex- 



