220 NEW YORK STATE MUSEUM 



Odonata/ I came to the conclusion that our hypothetical type 

 wing did not represent all the venation of the primitive insect 

 wing, but only the main skeleton of it. That the longitudinal veins 

 of that type were possessed by the primitive insect I do not doubt: 

 they represent the main lines of chitin deposition along primeval 

 tracheae; but the interspaces between these veins were occupied, 

 I believe, by a more or less irregular meshwork of cross veins, 

 which disappear with the progressive differentiation between strong 

 veins and thin membrane. Redundant cross veins are still char- 

 acteristic of many generalized insects, and were so of most of the 

 older fossils known. I have given in the paper just cited [p. 725- 

 28] a theory as to the mode of differentiation of strong cross veins 

 in the dragon flies. 

 There is much less 

 evidence as to how 

 the reduction may 

 have occurred in the 

 Diptera; but I have 

 no doubt that the ^'^- '' 



supernumerary cross veins and spurs of veins, so common in 

 Tipulidae, indicate the location of some few remnants of the large 

 numbers that were probably possessed by the early neurop- 

 teroid ancestors of the Diptera. It may be assumed that in any 

 process of reduction cross veins favorably situated, joining the 

 principal veins advantageously, would tend to grow stronger, while 

 others, less favorably situated in intervening spaces, would tend 

 to weaken and disappear. 



I have drawn and present in figure 12 a typical Tipulid wing 

 in which the principal veins with their full complement of branches 

 are represented in solid black, and the typical cross veins are 

 represented in double contours. This wing is based on a tracing 

 of the wing of Macrochile [pi. 14, fig. i] and differs very little 

 therefrom. Then, in order to see what sort of wing it would be if 

 all the supernumeraries occurring anywhere in any crane fly should 

 appear together, I located these supernumeraries, all in their 

 proper places, one by one, and I represent them then in dotted 

 lines in this figure. How like a Panorpid wing is the result! If 

 one compares it with the wing of Bittacus, for example, he will 

 see that the differences are very slight, and are confined chiefly 

 to the anal area. There is the same type of branching of all the 



^U. S. Nat. Mils. Proc. 1903. 26703-64. A Genealogic Study of Dragon 

 Fly Wing Venation. 



