BY R. J. TILLVARD. 705 



M 5 forming the upper arm. Cu, the lower, and the stem of the 

 Y being the fused vein M.g+Cuj, which forks again distally. 

 Cubitus three-branched, Cuj forking distally after fusion with 

 ^5, ^ u 2 remaining weakly formed and simple. Anal veins 

 three in number, all separate, either forked or simple. Convex 

 reins R, M5+CU1 and the three anals. Concave veins Se, M 1 _ 4 

 and Cu 2l Cross-vein system consisting of very weakly formed 

 cross-veins, more or less irregularly placed, and not in any 

 special positions of mechanical advantage. 



Wing-coupling apparatus (24) complete, the forewing with 

 jugal lobe and bristles, the hind with humeral lobe and frenulum. 



Wing-trichiation (25) showing both microtrichia and macro- 

 triehia, the former all over the membrane on both sides, the 

 latter confined to the main veins and their branches, including 

 the costal veinlets, and to the archedictyon, which is more or 

 less aphantoneuric. 



Fore and hind wings closely similar in shape and venation, 

 but the latter somewhat shorter than the former, more weakly 

 chitinised, and with somewhat shorter Sc. 



In repose, the wings are held roof-wise over the back of the 

 insect (stegopterous position) . 



Table of the Characters of the Wings for the Archetypes of 

 the Complex and its Orders. (Table v.) 



In the Table here given, the characters of the wings for the 

 various Archetypes constructed in Sections viii.-xvi., and for 

 the Archetype of the whole Complex, are arranged together for 

 comparison. For each character selected, the most archaic 

 condition is indicated by the letter A. This is usually only 

 contrasted with a single specialised condition, represented by 

 the letter B. In the case of characters in which a series of 

 evolutionary stages can be recognised, these are represented by 

 the letters A, B, C. . . ., in ascending order of special- 

 isation. 



For the purpose of comparing the venations of the various 

 Archetypes, their respective Comparative Archaisms may be 

 calculated. These are defined as "the percentage of archaic 

 characters retained by the given Archetype." The Comparative 

 Archaism for the Archetype of the Complex is, of course, 100, 

 since this type contains all the known archaic features. In 

 calculating the percentages for the other Archetypes, the follow- 



