248 THE WINGS OF PLECOPTERA 



Enderlein has introduced a new terminology of the veins of the anal 

 area, which I thinlc is unfortunate, as it tends to confusion. The veins of 

 this area of all orders of insects have long been known as the "anal veins." 

 When Comstock and Needham deterinined that these veins were typically 

 three in number, we designated them as the ^^^5^ anal (ist A), the second 

 anal {2d A), and the third anal {jd A) respectively. This preserved the 

 term anal, b}^ which they were generally known, and at the same time 

 afforded a specific designation for each. 



Enderlein restricts the term anal (an) to the first anal vein; and desig- 

 nates the second anal vein the axillary (ax), and the third anal vein the 

 accessory (acce) . He numbers the branches of the axillary vein from before 

 backward, and those of the accessory vein in the opposite direction. 

 (Zool. Anz. Vol. 28 p. 810). 



(e) THE PRIMITIVE PLECOPTEROUS TYPE OF WINGS 



The logical method of determining the various ways in which the wings 

 of the different members of an order of insects have been specialized is 

 to discover what is the most generalized type of wing-venation to be 

 found within the order and then to trace the various ways in which this 

 type has been modified in the different divisions of the order. This 

 method has been followed in the preparation of several of the chapters of 

 this book. 



In carrying out this method the t3rpe of wing-venation that most closely 

 resembles the hypothetical primitive type (Fig. 6, p. 16) is considered the 

 most generalized and is used as a starting point from which to trace the 

 various methods of specialization found within the order. 



In my efforts to apply this method to the study of the wings of the 

 Plecoptera I have found what, at first, was a most perplexing aiTay of facts. 

 Forms were found that appeared to possess a generalized type of wing- 

 venation. But when these forms were compared with closely allied forms, 

 other species of the same genus for example, it was found that certain of the 

 supposed generalized features were of little taxonomic value.* 



The lack of stability of the wing-venation is most apparent in the 

 number and distribution of the cross-veins and in the number and courses 

 of the branches of the longitudinal veins near the margin of the wings. 

 This is especially true of the secondary branches of the radial sector and 



*The lack of stability of the wing-venation of stone-flies is apparent to any one 

 that studies the order carefully. Ris ('96) in writing of the genus Dictyopteryx, after 

 referring to the fact that it is practically impossible to find two specimens of the same 

 species with identical wing-venation, and that seldom individuals are found that show 

 the same network of veins in the wings of the two sides, remarks: "Es sicht so aus, 

 als ob sich diese Thiere fur die wcnigen Tage, die sic als Imago zu leben haben, und 

 fur den geringen Gebrauch, den sic von ihren Flugeln machen, gar nicht den Luxus 

 eines streng gesetzmassig ausgebildeten Aderwerks gestatten konnten." 



