THE FLIES THAT CAUSE MYIASIS IN MAN 



21 



of which the radio-medial (r-m) and the medio-cubital (m-cu) need 

 to be mentioned. 



The more primitive dipterous wing (fig. 3) is so close to the hypo- 

 thetic-ally primitive type that it presents relatively little difficulty in 

 its interpretation. The muscoid wing ( fig. 4) can easily be understood 

 if one considers that its venation is a reduction of the more primitive 

 type through the disappearance of certain veins and the fusion of 



Figure 3. — Wing of Thereva, illustrative of the more primitive type of venation. 

 h t sc. rn 



Figure 4. 



cu2+2nd a^ x m3+cui l cubitulus 



-Wing of CaUitroga americana, illustrative of the museoid type. 



others. According to the Comstock-Needham system, the symbols 

 used to indicate such fusion simply compound the fused elements. 

 For example, r 2+3 means the undivided second and third branches of 

 the radius: ?n^n/ 1 means the fusion of the third branch of the media 

 with the first of the cubitus. In the higher muscoids, vein 0&i +2 , after 

 its separation from m,. bends, sometimes broadly, sometimes abruptly, 

 toward the radius: when this bend is well marked, it is known as the 

 cubitulus. 



Certain other structures on the wing or associated with it are of 

 taxonomic importance. Series of setulae may occur at various places — 

 for instance, on the stem of the radius basad of the humeral cross vein, 

 on vein i\ beyond the origin of the radial sector, or on vein r M 



