THE WINGS OF HYMENOPTERA 371 



which should be consulted by anyone making a study of the wing-venation 

 of members of this suborder. But I shall have occasion, in the course of the 

 later discussion, to quote some of his results. 



Passing to the suborder Clistogastra, we find it comparatively easy to 

 determine the homologies of the wing-veins in many forms, that is in those 

 in which the venation is not greatly reduced, by making use of the data 

 obtained in the study of the Chalastogastra. But there are many forms 

 with greatly reduced wing-venation in which the problem is exceedingly 

 difficult . Much has been done in this field by Professor J. Chester Bradley, 

 but unfortunately only a part of his results has been published. 



In his monograph of the Evaniidse (Bradley '08), Professor Bradley has 

 figured all of the types of wings known to occur in this remarkable family. 

 In another very extended work, entitled The Wings 0} Hymeyioptera with 

 partictdar reference to the Ichneumon Flies, some of the more perplexing 

 problems that have arisen in the study of the modifications of the venation 

 of the wings of the Hymenoptera are discussed in a very thorough manner; 

 but this work is not yet published. 



The m.ore important of the methods by which the primitive type of 

 wing- venation has been modified in the Hymenoptera are the following: 



A reduction in the number of the wing-veins by the atrophy of one or 

 more veins. 



A reduction in the number of the wing-veins by the coalescence of 

 adjacent veins in one or more areas of the wing. 



A change in the course of a vein by the coalescence of its base with an 

 adjacent vein. 



Changes in the courses of veins by the coalescence of the tip of each 

 with an adjacent vein. 



The formation of serial veins. 

 . The following examples will serve to illustrate the results of the modifi- 

 cation of the primitive type of wing-venation by these several methods. It 

 is an interesting fact that the wings of the most generalized of living Hymen- 

 optera show modifications by each of these methods. The wonderfully 

 modified wings of the more specialized Hymenoptera are merely the result 

 of carrying to an extreme methods of modification already inaugurated in 

 the most primitive Hymenoptera known to us. 



Reduction by atrophy — In the Hymenoptera one result of the specializa- 

 tion of the venation of the wings is a reduction of the number of wing-veins; 

 in no case are either accessory veins or intercalary veins developed; and 

 even in the most generalized members of the order known to us not all of 

 the wing- veins are retained. 



The reduction in number of the wing-\'eins, however, is slight in the 

 more generalized members of the order; as already indicated, in some only 

 vein R2 is lacking, in others, only veins Cuo has been lost. This refers to 



