348 



THE WINGS OF DIPT ERA 



accessory nor intercalary veins are ever developed, and only the principal 

 cross-veins are present. In more specialized forms the typical atTangement 

 of the veins has been greatly modified by the approaching and coalescing 

 of the tips of adjacent veins. Remarkable instances of this occur in the 

 Nemistrinidse (Fig. 358). 



(6) THE METHODS OF SPECIALIZATION OF THE WINGS OF THE DIPTERA 



In the discussion of the methods of specialization of the wings of the 

 Diptera reference will be made only to the specialization of the fore wings, 

 as a discussion of the structure of the halters does not fall within the scope 

 of this work. 



Ordinal specializations. — In all Diptera the venation of the wings is 

 more or less reduced, in none has there been a specialization b}^ addition. 



/?. R, 



?d A I si A C»2 ^'^i 

 Fig. 359. — Wings of a caddice-fly. 



Even in the most generalized forms, with the possible exception of Proto- 

 plasa, media is only three-branched ; and the anal area is always more or 

 less reduced, that is, in none are there three well-developed anal veins. 



The loss ojvein Mi. — A study of the method of branching of media in the 

 more generalized forms, as, for example, in Rhyphus (Fig. 357), shows that 

 veins Mi and M2 are preserved distinct, and that the third branch of this 

 vein is cither vein M3, in which case veins M4 and Cui have coalesced; or 

 vein M3+4, veins M3 and M4 having coalesced. 



