THE PALEONTOLOGICAL DATA 



95 



Fig. 85. — Diaphanoptera Munieri 

 (After Handlirsch). 



This condition is paralleled by the recent Diptera, among which the 

 ven^ generalized Protoplasa (Fig. 360) has a distinctly branched subcosta, 

 while in most members of the order 

 this vein is simple. 



In conclusion one can say that 

 the forking of the subcosta is a very 

 ancient feature of this vein; whether 

 it existed or not in the stem form of 

 the winged insect series remains to 

 be determined. Obviously nothing 

 would be gained by representing it as a simple vein in our diagram of the 

 hypothetical type of primitive wing-venation. 



The evolution of the radius.— As the result of our studies of recent 

 insects Comstock and Needham concluded that the primitive form of the 

 radius was that represented in our hypothetical type of primitive wing- 

 venation (Fig. 6) . We were led to this conclusion by the fact that in the 

 more generalized members of several of the orders of insects this type of 

 radius exists. Among these are the Homoptera, Lepidoptera, Trichoptera, 

 Diptera, and Neuroptera. Detailed discussions of examples are given in 

 later chapters. And in each of those orders where another type of radius 

 exists, it is easy to see how it has been derived from the hypothetical typical 

 form by well-known methods of specialization. 



Let us pass now to an examination of the paleontological data bearing 

 on the primitive form of the radius. There can be no doubt that the first 

 forking of the radius, by which this vein becomes divided into two parts, 

 which are now known as veins Ri and the radial sector, or vein Rg, respec- 



Fig. 86. — Diagram representing the two types of the radial 



sector; a, the pectinate type; b, the dichotomously 



branched type. 



tively, is a very ancient characteristic of this vein. This forking is so 

 constantly present in the fossils to be discussed later that it is unnecessary 

 to cite examples of it here. The part of the radius that requires special 

 study is the radial sector. 



