THE WINGS OF DIPTERA 



361 



The difference in the application of the terms first submarginal and 

 second submarginal in the terminologies of Osten-Sacken and Williston 

 arises from the fact that in each case the cell lying next to the marginal cell 

 is termed the first submarginal; but this is not the same cell in the two 

 genera used to illustrate their terminologies. The genus used by Osten- 

 Sacken is a Tipulid; and in all Nematocera that have a three-branched 

 radial sector veins R2 and R3 remain distinct; hence the cell next to the 

 marginal cell is cell Ro. On the other hand the genus used by Williston 

 belongs to the Brachycera ; and in this division of the order veins R2 and R3 

 coalesce throughout their entire length, and consequently the cell immed- 

 iately behind the marginal cell is cell R3. 



