BY R. J. TILL YARD. '03 



bound to come to is that this Archetype was essentially of a 

 Prohemerobiid type, but with R 4+5 still diehotomieally branched, 

 as in Text-fig. 109, which may be taken as the forewing of the 

 Archetype as well as that of a typical Prohemerobiid wing. 

 M l _ i was tour-branched, and Cu three-branched. Terminal 

 splitting or twigging of the veins is typical of the Order; and 

 this character is therefore included in the Archetype. The 

 system of costal veinlets also tended to split at the tips. The 

 cross-vein system was probably very primitive, but showed a 

 slight specialisation, as in the Megaloptera, in having only three 

 cross-veins between R x and Es, and probably also only two (sh 

 and sc-r) between Sc and Rj. 



It will now be clear that there is only a single character in 

 the wing-venation of the Megaloptera which is more highly spe- 

 cialised than the corresponding one in the Archetype of the 

 Planipennia, viz., the absence of any remnant of M 5 in the fore- 

 wings of the former. Apart from this, the Planipennia can be 

 directly derived from the Archetype of the Megaloptera by 

 further increase in the tendency to pectination and addition of 

 branches to Rs, and by the beginnings of the terminal splittings 

 of the veins. Thus the two Orders, in respect of their wing- 

 venation, are barely distinct, and may be shown as a dichotomy 

 from a common stem, which must itself have been derived from 

 somewhere along the original main stem of the Complex, pro- 

 bably somewhat before the point indicated by Belmontia in Text- 

 fisr. 112. The tw r o Orders are more closely related than are the 

 Trichoptera and Lepidoptera; and those who prefer to merge 

 them into a single whole, as two Suborders of a single Order 

 Xeuroptera, are quite logical in doing so. We shall continue 

 to keep them distinct, for purposes of discussion, throughout 

 this research, and shall only make a final decision on the ques- 

 tion, when the wdiole of the evidence bearing upon it has been 

 dealt with. 



Section xvii. Phylogestetic Results. 



(Text-figs. 38, 111, 112.) 



We may now summarise the results of the preceding Sections 

 as briefly as possible, with a view to deducing some phylogenetic 

 conclusions therefrom. We shall arrange these as follows:— 



(1) Construction of the Venation of the Archetype of the 

 Complex . 



