BY R. J. TILLYARD. 053 



Hence the terminology M4 must either be accepted throughout 

 the Order, or else it must be altered throughout to m-cu. 



It is left optional for anybody, who prefers this latter alter- 

 native, to reject the account given of the structure and evolution 

 of the Distal Y-vein in Section vi., and to alter the Tables on 

 pp. 650, 706, to suit the new view. The net results of the 

 alteration would be that the Hepialidae would have to be re- 

 garded as somewhat more highly specialised, the Jugo-frenata 

 slightly more archaic, than the percentages in Table iii. would 

 indicate; and also that the Lepidoptera, as a whole, would be 

 brought slightly nearer to the Trichoptera, seeing that the con- 

 dition of M in both wings of the former will then become the 

 same as that in the hind wing of this latter Order. 



Suborder Heteroneura. 



The problem of the evolution of the Heteroneura is a most 

 fascinating one, and vitally concerns us here, in so far as it 

 must be quite evident that no single existing family of the 

 Homoneura at the present day can possibly represent the ori- 

 ginal stem of the Lepidoptera, from which both Homoneura and 

 Heteroneura, as we know them to-day, arose. All we can be 

 certain of is this: — that the Heteroneura are derived from a 

 Homoneurous ancestor of which no completely generalised des- 

 cendant e.rists to-day. The task of determining the characters 

 of that ancestor is only to be undertaken by a careful examina- 

 tion of all archaic existing types, together with any fossils 

 known; and the Archetype of the Order must be that type which 

 combines in itself all the archaic features of this ancestor, as 

 well as those of the Homoneura. 



That being so, it is necessary here to examine carefully the 

 following groups: (i.) the Jurassic fossil family Palaeontinidae, 

 ( ii. ) the Cossidae, (iii.) the superfamily Tortricina, (iv.) the 

 superfamily Tineina, (v.) the Castniidae, (vi.) the superfamily 

 Psyehina, and (vii.) the superfamily Pyralidina. To these I 

 have added the Butterflies, whose phylogeny is a fascinating 

 problem of its own, as yet unsolved. 



The publication of Dr. A. J. Turner's paper on the vena- 

 tion of the Cossidae (32) marks a great advance in our know- 

 Ledge of the phylogeny of the Heteroneura, and I shall not 

 hesitate to refer to it whenever necessary, especially as a pre- 

 vious paper of my own (13) helped to stimulate Dr. Turner in 

 his work, and as this author adopted the main contentions made 



