97 



IDENTIFICATION OF THE WING-VEINS AND OF THE CELLS OF 

 THE WING IN DIPTERA. 



As the chief object of the following work is to give the 

 student training in tracing the homologies of wing-veins, 

 comparatively little information will be given directly. The 

 student will be furnished in each case with the wing to be 

 studied, and his studies should take the following course : — 



Directions for the study of wings. — Make a drawing 

 of the wing, based upon a careful study of it with a com- 

 pound microscope, using a low power. The drawing should 

 be first made with a pencil ; after it has been criticised by 

 the teacher, the lines should be inked; ink the lines repre- 

 senting the media with red ink, use black ink for the re- 

 mainder of the wing, including the medial cross vein. Make 

 the drawing on a sufficiently large scale so that each vein 

 can be represented distinctly ; in most cases the drawings 

 should be somewhat larger than Figure 3. 



Number each vein and cell of the wing. 



Note the more important features of its venation, and 

 especially the more important departures from the primitive 

 type of the order as indicated by the generalized form first 

 studied. In the Diptera the wing of Rhyphns (Fig. 2) may 

 be used as a generalized type, although in certain respects 

 other wings will be found to be more generalized. 



The following are some of the more important points to be 

 noted : Whether the subcosta is simple or forked at the tip , 

 the number of the branches of the radius ; in this connection 

 determine which of the radial cells has been obliterated by 

 the coalescence of branches of the radius (study Fig. 5) ; the 

 position of the radio-medial cross-vein ; the number of the 

 branches of the media (in none of the common Diptera has 

 the media more than three branches ; and the mode of dis- 

 appearance of vein M^ in this order has not been determined 



