376 THE WINGS OF HYMENOPTERA 



for example the course of \'ein Mi in Apis (Fig. 396). Here this vein extends 

 towards the base of the wing, with the result that the free part of it appears 

 to be a continuation of the cubitus. 



Serial veins. — Perhaps the most astonishing and perplexing of the 

 results that have followed the changes in the courses of veins in the wings 

 of the Hymenoptera are those that have resulted in the formation of serial 

 veins ; that is veins that appear to be simple veins but which in reality are 

 compound veins composed of sections of two or more ^'eins joined end to 

 end. 



Serial veins are discussed in Chapter III (page 69). In addition to the 

 serial vein described there, vein ^n & M2 of the braconid wing, the follow- 

 ing examples may be cited. 



In the fore wing oiApis (Fig. 396), the cubitus appears to extend from 

 the base of the wing to a point near the middle of the wing. But, as shown 

 above, only the basal part of this vein is cubitvis, the distal part being vein 

 M4. If reference is made to this vein as a whole, it should be designated as 

 vein Cu & M4. 



In the case just cited the fomiation of the serial vein is the result in a 

 change in the course of one element of it. Another method of the formation 

 of serial veins is by the atrophy of a section of a vein, which leaves the 

 terminal portion of the vein stranded upon some other vein. Vein m & 

 M2 of the braconid wing was formed in this manner. 



A remarkable instance of the atrophy of a section of a vein and the 

 consequent formation of a serial vein that has the appearance of being a 

 simple one is that described by MacGillivray ('06) as the switching of the 

 base of the radial sector. This example of the formation of a serial vein is 

 of especial interest; for this switching of the base of the radial sector has 

 occurred in the wings of nearly all members of the suborder Clistogastra, 

 and is found in only a few members of the suborder Chalastogastra. 



A very complete series illustrating the switching of the radial sector was 

 found by MacGillivray and is shown in Figure 397. Before studying this 

 series, however, let us examine the fore wing of Paniphilius (Fig. 391) and 

 note the point of origin of the radial sector and the position of the radial 

 cross-vein in what we have accepted as a typical hymenopterous wing. 



An examination of this wing and of the very extended series of wings of 

 Chalastogastra figured by MacGillivray, shows that the radial sector 

 separates at or before the base of the stigma, and that the radial cross-vein 

 extends from near the middle of the stigma or from a point be^'-ond the 

 middle, in a more or less nearly transverse direction, to the radial sector. 



In Figure 397, a, 6, and c show a part of the fore wing of three members 

 of the Cephidae, one of the more specialized families of the Chalastogastra ; 

 and d represents the same part in Oryssus, of the Oryssidae, the family in 

 which the greatest reduction of the wing-venation found in the Chalasto- 



