()38 THE PANORPOID COMPLEX, iii., 



more specialised, being about level with the Hepialidae in the 

 percentage of archaic characters which they possess. The 

 Mnesarchaeidae are the most highly specialised of all the Hoino- 

 neura . 



The manifest agreements between the venational schemes of 

 the Archetypes of the Jugo-frenata and the Trichoptera are 

 clearly of the utmost importance, since it is on these that Corn- 

 stock (15) has removed the former to the latter Order. They 

 may be stated as follows : — 



(1) Sc and R 1 are distally forked. 



(2) The branches of Rs are four in number and dichotom- 

 ously arranged. 



(3) The radial cell is closed distally by ir. 



(4) The cubito-median Y-vein is completely formed. 



(5) The cubitus is three-branched, Cuj being forked distally. 



(6) The anal veins of the forewing form a double loop or Y- 

 vein . 



(7) In the hindwing, 1A fuses with Cu 2 for a short distance 

 not far from the base, and then diverges from it and runs 

 separately to the wing-border. 



(8) The cross-vein system in the Jugo-frenata is closely similar 

 to that of most archaic Trichoptera, although im is always ab- 

 sent. In particular, ia 1 in the hindwing is longitudinally placed. 



With one exception, all the above characters are to be found, 

 not only in Trichoptera and Jugo-frenata, but also in either (a) 

 other Panorpoid Orders, or (b) other Lepidoptera. The excep- 

 tion is (6) . The double Y-vein formed by the looping up of 

 the three anal veins is peculiar to the Trichoptera and to the 

 genera Mnemonica and Sabatinca amongst the Jugo-frenata. In 

 the other genera, it is either absent (replaced by the single 

 Y-vein usual in Lepidoptera) or occasionally more or less clearly 

 formed. If the complete double-Y formation is the more archaic 

 condition, then it is clear that it must have been inherited from 

 the common ancestor of both Trichoptera and Lepidoptera; 

 but, while the Trichoptera have retained, and, in many cases, 

 elaborated it, the Lepidoptera, on the other hand, almost imme- 

 diately began to lose it, through degradation of the vein 3A. If, 

 however, the single Y-vein be the older formation, then the al- 

 ready present tendency towards further specialisation must have 

 produced the double-Y formation independently in the Trichop- 

 tera and in those Jugo-frenata which possess it, while most of' 



