18 



SOME ASPECTS OF MORPHOLOGY 



with one another, probably because this condition is regularly 

 apparent in certain orders only. Also the theory that the 

 ancestral winged insects had the richest venation, from which 

 later types were derived by reduction, was not accepted. While 

 we owe to Comstook and Needham what is one of the greatest 

 advances ever made in the study of insects, the importance of the 

 earlier fundamental work of Redtenbacher should not be over- 

 looked. The Comstock-Needham system (Fig. 7) is now well 

 known and, for this reason, it is not necessary to recapitulate here 

 what has often been described since in text-books. It will be 

 necessary, however, to discuss certain more recent investigations 

 on wing venation and their bearing upon the general theory. 



The contributions of Tillyard, dating from 1919, have greatly 

 extended our knowledge of the subject in many orders, and this 



Cii, 



CU-TA 



Fig. 8. Diagram of the branching of the cubital vein ; A, according 

 to Comstock and Needham ; B, according to Tillyard and later 

 authorities. Cu, cubital vein ; \A, first anal vein. 



author's detailed studies of early fossil types shed further light 

 on venation from the palseontological aspect. In his papers on 

 the Panorpoid complex, ^ Tillyard arrived at the conclusion that 

 Comstock and Needham's hypothetical type is not entirely 

 applicable as one from which the venation, of the orders forming 

 this complex, was presumably derived. The most important 

 feature brought to light by Tillyard 's earlier discoveries refers to 

 the composition of the cubital vein. He was able to show on 

 ontogenetic grounds that this vein is primarily three-branched, 

 and not two-branched as Comstock and Needham believed 

 (Fig. 8). The vein which the latter authorities regarded as the 

 first anal, which had become secondarily associated with the 



^ The Panorpoid Complex includes the Mecoptera, Neuroptera, Trichoptera, 

 Lepidoptera and Diptera, together with related extinct orders only known as 

 fossils. 



