614 THE PANORPOID COMPLEX, iii- - 



distal forking. They also agTee with the Mecoptera in the 

 generalised condition of the anal area of the forewing. This 

 character marks them off most strongly from the Triehoptera, in 

 which the three anal veins form a double Y-vein, and from the 

 Diptera, in which the anal area is narrowed, and the anal veins 

 much reduced . 



It will be clear from the above evidence that the Paratrichop- 

 tera must be regarded as a somewhat specialised side-branch fx*om 

 the old Mecopterous stem, and that they arose at a time when 

 the basal branch of Sc, preserved in Aristopsijehe, had not been 

 entirely eliminated from the venation. Since this branch of 

 Sc has not yet been noticed in any true fossil Mecoptera, al- 

 though a much more complete branch is present in the Triassic 

 Protomecoptera (Section x.), we should probably be on very 

 safe grounds in assuming that the Paratriehoptera, like the Pro- 

 tomecoptera, must have already become differentiated in Upper 

 Permian times. Thus, representatives of the Order may con- 

 fidently be expected to be found, when more complete investiga- 

 tions of the beds of this age, in Australia and elsewhere, can be 

 carried out. 



The great importance of the Paratriehoptera as an Order is 

 that they do most certainly indicate the line of descent of the 

 Diptera from ancient Mecopteixras-like forms. A comparison 

 of the Archetypes of the two Orders Paratriehoptera and Diptera 

 will be made in the next Section, and will clearly show how 

 simple a derivation of the Diptera from this Triassic Order can 

 be proved, as far as the venation of the forewing is concerned. 



Section xii. The Venation of the Diptera. 

 (Text-figs. 43, 48-50, 66-70.) 



The determination of the venation of the Archetype of this 

 huge Order is a matter of little difficulty, in spite of the im- 

 mense number and variation of the venational types existing 

 within it at the present day. As the pupal wings are mero- 

 tracheate, — and, indeed, little is known about them at all in 

 comparison with the pupal wings of the dominant holotracheate 

 Order Lepidoptera, — I have not been able to attempt a complete 

 analysis of the venational types of the various archaic families 

 within the Order, as I have done in Section xiv. for the Lepi- 

 doptera. Such an attempt, in the case of the Diptera, would 



