396 THE WINGS OF INSECTS 



with red ink. Make the drawings on a sufficiently large scale so that each 

 vein can be represented distinctly, and on paper uniform in size with that 

 used for the printed figures of wings used in this course. 



Letter each vein and cell of the wing, using black ink for the veins and 

 red ink for the cells. 



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 Rhyphus 

 (Fig. 410) 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. 409); the position of the radio-medial cross-vein; the number of the 

 branches of the media; the division or not of cell M2; the presence or 

 absence of cell M3 ; the courses of the branches of the cubitus ; the extent 

 of the anal furrow, which is a vestige of the first anal vein; and the extent 

 and course of the second anal vein. 



Wing of a tabanid.— A specimen of one of the horse-flies, Tabanus, will 

 be given the student for examination. Observe the subcostal fold, and note 

 that this corrugation stiffens the wing. 



Make a drawing of a mounted Tabanid wing, which will be furnished 

 on application to the instructor. Note that in the mounted wing the sub- 

 costa is more or less concealed by the radius, although the two veins are 

 distinct, as was seen in the unmounted specimen. Represent these two 

 veins as slightly separated in your drawing. 



Note a case of coalescence of veins not exhibited by Rhyphus. 



In the description of this wing, state in what respect it is more general- 

 ized than that of Rhyphus, and in what respect it is more specialized. 



Wing of an asilid. -A wing of a robber-fly of the genus Erax will be 

 used as an example. 



There is a spur projecting from one of the branches of radius in this 

 wing. This is a secondary development. Such spurs are not uncommon in 

 the Diptera ; there is one near the base of the radial sector in the wings of 

 Proioplasa fitchii, (Fig. 415). Not all spur-like veins are secondary develop- 

 ments; in many cases a spur is a vestige of a vein that is partly atrophied. 



Wing of abombyliid. — The example used is a wing of Pautarhes, one of 

 the bee-flies. 



Wing of a scenopinid. — The wing used is that of a common window-fly, 

 Scenopinus. 



Wing of an empidid. — The wing used is that of Rkaniphomyia, one of 

 the dance-flies. 



