Vol. 1.] Wood ivorth. — Wing Veins of Insects. 85 



PART III.— TYPES OF VENATION. 



In the discussion of the types of venation we shall, for con- 

 venience, group insects into three series, which may be desig- 

 nated the Neuroptera, Elytroptera, and Neoptera. These are 

 not offered as natural groups, but merely convenient assem- 

 blages of groups from a pterological point of view. 



NEUROPTERA. 



Neuroptera is used in the Linna^an sense, but includes all 

 the older fossil forms that have been assembled under the 

 name Paheodictyoptera by Scudder, thus representing the 

 primitive winged insects and all the derived groups excepting 

 the three with the thickened front wings and the three most 

 recently evolved orders. 



The two problems that present themselves most prominently 

 to the student in this group are, first, the treatment to be 

 accorded to ancient venations, and secondly, the criteria for 

 the recognition of the separation of distinct types. 



ANCIE.NT VENATIONS. 



The study of venation is nearly coextensive with that of the 

 classification of insects. Not only is the venation correlated 

 with the systematic position of an insect, but all the problems 

 involved in the grouping of organisms apply with equal force 

 to the interpretation of the specialization of such an organ as 

 a wing. 



The venation of the most ancient fossil remains of insects 

 has not thus far yielded as satisfactory evidence on the early 

 course of the evolution of venation as it has been expected to 

 give. For this reason it has not figured very conspicuously in 

 the discussions of venation. Before the close of the Paleozoic 

 era, insects were evidently already abundant and varied in 

 form. The remains preserved to us in the rocks are every- 

 where acknowledged to be extremely fragmentary, and the 

 relation of these ancient forms to the existing groujis is a 

 matter of controversy. 



