412 THE WINGS OF INSECTS 



the first anal vein being its most obvious element (Fig. 425), although it is 

 really vein M4 + Cui + Cu2 + ist A. 



The more important methods by which the primitive type of wing- 

 venation has been modified in the Hymenoptera are the following : 



(a) A reduction in the number of the wing-veins by the atrophy of one 

 or more veins. The loss of vein Ro in the fore wing of Pamphilins (Fig. 

 423) and of vein Cuo in the fore wing of Macroxyela (Fig. 424) are illustra- 

 tions of this. 



(6) A reduction in the number of the wing-veins by the coalescence of 

 adjacent veins in one or more areas of the wing. Examples of this will be 

 indicated later. Such a reduction has nearly occurred in the fore wing of 

 Pamphilius where the first and second anal veins coalesce for the greater 

 part of their length. 



(c) A change in the course of a vein by the coalescence of its base with 

 an adjacent vein. The course of media in the fore wing of Pamphilius 

 (Fig. 423) has been modified somewhat by its coalescence with radius; this 

 modification has been carried much farther in some foiTns to be studied 

 later. 



(d) A change in the course of a A^ein by the coalescence of its tip with 

 an adjacent vein. The changes in the direction of the branches of radius, 

 media, and cubitus described above illustrate this. 



(e) The formation of serial veins. Examples of this will be presented 

 later. 



The strident who has followed this discussion and has understood it will 

 be prepared to make original investigations of the venation of the wings of 

 Hymenoptera. But no student should take up the work indicated below 

 before everything in this discussion is clear to him. 



Study the fore wings of the insects named below. It is not best to 

 attempt to determine the homologies of the veins of the hind wings at first, 

 owing to the great reduction of wing-veins that has taken place in these 

 wings. The directions for the study of wings given on page 395 will apply 

 here except that Figures 425 and 426 instead of Figure 410 will be used for 

 comparison. 



Examples of comparatively generalized hymenopterous wings. — The 



fore wing of a saw-fly and the fore wing of a siricid will be used as examples 

 of comj^aratively generalized hymenopterous wings. In neither of these 

 wings is the venation as generalized as in Pamphilitis or in Macroxyela. 



A fore wing of Pteronidea ribesii. — A fore wing of the currant saw-fly, 

 Pteronidea ribesii, is selected for the study of an actual hymenopterous 

 wing; a mounted wing will be furnished for study; printed figures of other 

 wings to be studied will be issued as needed. 



Make a drawing of the wing. 



