THE WINGS OF DIPT ERA 359 



"This study of the homologies has two distinct aims in view: the 

 scientific aim of showing that the ground-plan of the venation is the same 

 in all of the families of the order; and the practical aim of adopting a 

 terminology for descriptive purposes. We cannot carry out a terminology 

 on solely theoretical grounds; we will have to vary the details of it accord- 

 ing to the peculiarities of structure occurring in different families, the main 

 plan remaining the same. This is done in all the departments of zoology, 

 and I do not see why the venation of the Diptera should be treated differ- 

 ently." 



Owing to the lack of uniformity in the terminologies used by different 

 authors and to the fact that even in the writings of a single author homol- 

 ogous veins are designated differently in the discussions of different families, 



5-.. . TT— ^ '^ 



Fig. 379. — Wing of Tabanus (After Williston). 



it is necessary for the student using any of the works in which the uniform 

 terminology has not been adopted to make a study of the system used in 

 that particular work. 



The system that has has been most used in this country is that which 

 was adopted by Loew ('62) and modified by Osten-Sacken ('69). Figure 

 379 from Williston ('08) illustrates this system as applied by him to the 

 wing of Tabamts. In the following table this system and that of Redten- 

 bacher are compared with the uniform terminology. 



Redtenbacher in his efforts to recognize the concave veins IV and VI of 

 his system was led into inconsistences in his determinations of the homolo- 

 gies of the branches of media. The equivalents given in the following 

 table are based on his figure of the wing of Stratiomys. 



