342 THE BIOLOGY OF INSECTS 



history of the insects living around us to-day as to the 

 general course of their evolution. 



The extreme modification of the wings among the Diptera 

 renders the order one of exceptional interest to the student 

 of insects. The Upper Triassic beds of Queensland have 

 yielded fossils representing four genera (Aristopsyche and 

 others) which Tillyard places in a special extinct order, the 

 Paratrichoptera, arising, as its name implies, along with the 

 ancestral Trichoptera from the Paramecopteroid stem. 

 These Paratrichoptera are believed by Tillyard to have 

 been actually '' ancestral to the true Diptera." All their 

 wings that have been examined are apparently forewings, 

 intermediate as regard neuration between the Mecopteroid 

 and Dipteran type. Tillyard is of opinion that the hind- 

 wings of these insects were not very different from the fore- 

 wings ; we still have no definite information how they 

 became reduced and modified into the Dipteran halteres. 

 The oldest known fossils referable to true Diptera are from 

 European beds of Upper Liassic age, and these belonged to 

 the sub-order Nematocera and to those sections of the 

 Brachycera whose larvae (like the grubs of Nematocera) 

 have a definite head-capsule. The earliest known members 

 of the cyclorrhaphous Brachycera (flies whose larvae are 

 headless maggots) are of Tertiary age, and their fossil 

 remains come largely from the same beds as those in which 

 the great majority of fossil Lepidoptera are preserved. 



The Hymenoptera are, like the Diptera, one of the most 

 highly specialised orders of living insects. It is therefore 

 of great interest to find that some fossils from those Lower 

 Permian rocks of Kansas, which have yielded so much 

 information of the greatest importance to the student of 

 insects, prove to represent the ancestral stock of the Hyme- 

 noptera. These wings are referred by Tillyard to an extinct 

 order Protohymenoptera among whose members '' fore and 

 hind wings were of almost equal size and were not yet linked 

 together in flight by booklets." Tillyard places also among 

 the Protohymenoptera the only Carboniferous fossil (except 

 Metropator mentioned above) referable to the Endoptery- 



