358 



THE WINGS OF DIPT ERA 



The second anal vein is the most persistent of the three anal veins ; it 

 is well-preserved in many families; and is represented in several of the 

 figiires in this chapter. 



The third anal vein is well-preserved in comparatively few forms, 

 although a vestige of it exists in many. It is well-preserved in Tipida 

 (Fig. 377), and is fairly well-preserved in Stratiomyia (Fig. 378). 



The arctilus. — There is a well-developed arculus in the Diptera; but 

 owing to the reduced condition of the tracheation in this order the elements 

 that enter into its formation can not be definitely determined. In labeling 

 the cells at the base of the wing, I have assumed that the structure of the 



S c /?, R.., R, 



Fig. 378.- — Wing of Stratiomyia. 



arculus is the same as in those orders where its composition is well-known. 

 According to this interpretation veins R and M coalesce from the base of 

 the wing to the arculus; and, consequently, the cell behind the coalesced 

 veins R and M is I St cell M (Fig. 378). 



In many of the Diptera, the base of the free part of the media has 

 migrated along the arculus so far that it appears to arise from the cubitus 

 (Fig. 375)- 



The spurious vein. — In the Syrphidse there is a longitudinal thickening 

 of the wing between the radius and the media ; this is termed the spurious 

 vein (Fig. 376, s). 



(c) COMPARISON OF TERMINOLOGIES OF THE WING-VEINS OF THE DIPTERA. 



It is practically impossible to make in a single table a comparison of the 

 various terminologies of the wing-veins of the Diptera that have been used 

 by the prominent writers on this order. This is due to the fact that none 

 of the older authors succeeded in determining the homologies of the different 

 veins throughout the order; the result is that homologous veins are 

 designated differently in the discussions of different families. This was 

 frankly admitted by Osten-Sacken ('69, p. 32) in the following remarkable 

 statement. 



