THE WINGS OF HYMENOPTERA 363 



This determination was made by the writer, from an examination of the 

 wings of adult insects, and pubHshed in a text-book* before the ontogenetic 

 study of wings was undertaken by Dr. Needham and myself. 



The results of this later study did not modify the conclusions that I had 

 reached from the study of adults alone. In fact, we found, as will be 

 shown later, that the courses of the tracheae of the wings of hymenopterous 

 pupae have not been modified in the same way as have the courses of the 

 veins; and that, for this reason we are still forced to determine the homol- 

 ogies of the wing-veins in this order by a comparative study of the wings of 

 adult insects. 



An understanding of the hymenopterous type of wing-venation was not 

 derived from a study of the wings of Hymenoptera alone. Even in the 

 most generalized of the living members of this order, the wings are so 

 highly specialized that the homologies of certain veins would never have 

 been suspected but for help from another source. 



Fortunately the most characteristic method of modification of the 

 courses of the wing-veins in the H3^menoptera is illustrated by the wings of 

 certain Diptera also. And in the Diptera examples of ever}^ stage in the 

 modification of the courses of veins by this method can be seen ; while in 

 the Hymenoptera only the later stages are shown. 



Reference is made here to the coalescence of veins from the margin of the 

 wing towards the base of the wing. This results frequently in a branch of 

 a longitudinal vein becoming transverse, so that it appears like a cross-vein; 

 and in some cases, where the coalescence has been carried still farther, a 

 branch of a longitudinal vein has been so diverted from its primitive course 

 that it extends towards the base of the wing. Among living Diptera there 

 are preserv^ed examples of all of the stages of this modification of the course 

 of a vein. The series of figures illustrating the coalescence of veins Cu2 

 and 2d A (p. 355) shows this. 



With this data before tis let us proceed to an examination of h^onenop- 

 terous wings. The most generalized condition of the venation of the wings 

 that is known in the Hymenoptera occurs in the two genera Pamphilius, of 

 the family Lydidoe, and Macroxyela, of the family Xyelidae. There is 

 preserved in the fore wings of each of these genera of sawflies all of the 

 primitive wing- veins with a single exception ; and as it is not the same vein 

 that has been lost in the two genera, a figure of a typical hymenopterous 

 wing can be made from a study of the two. Figures 382 and 383 represent 

 such a wing; in the former the veins are'lettered; in the latter, the cells. 

 See also Plate X, where the courses of the veins are made more evident by 

 the use of alternating colors. 



The typical h\mienopterous wing represented in the accompanying 

 figures is a figure of the fore wing of Pamphilius (Fig. 391) except that vein 



*Comstock: A Majiual for the Study of Insects. (1895), pp. 603-607. 



