678 THE PAX0RP01D COMPLEX, iii., 



traces of M in both wings,* and a definite form of wing, with 

 regularly radiating veins from the cell as a common basis of 

 origin, is firmly established. There is a peculiarity of the 

 Thyrididae which is worthy of note, viz., that the splitting back 

 of the branch trachea?, originally only a specialisation of the 

 pupal wing, has reacted on the imaginal venation also, thus 

 throwing back the origins of most of the branch veins to points 

 nearer the base than they were in the ancestral condition. This 

 is well seen in Text-fig. 98, and is the principal cause of the 

 comparative shortness of the basal cell in this family and its 

 relatives, as compared with other groups. Compare, for in- 

 stance, the type of cell found in the Butterflies ( Text-figs . 99- 

 102) with that of the Thyrididae, and there can be no doubt 

 which of the two comes closest to the original condition, as re- 

 gards size. 



In the hindwing of Bhodoneura, 1A and 2A are fused together 

 very close to the base to form a small Y-vein. The vein below 

 this is the true 3A, homologous with that of the Cossidae and 

 che Tortricina. 



Unfortunately I have not dissected any pupae of Pyralididae, 

 though the family is abundant enough in Australia. In at- 

 tempting to keep this research down to a reasonable level, I 

 had to confine myself to studying only the more archaic families. 

 Having failed to obtain pupae of the Thyrididae, it will now be 

 necessary to turn to those of the Pyralididae for the elucidation 

 of a very important point, viz. the manner in which the ar- 

 rangement of the branches of Rs in the imaginal forewing has 

 been brought about. This piece of research must be left for a 

 future occasion; for, as far as I know, no descriptions of the 

 pupal tracheation of the Pyralididae have yet been published. 



The importance of this question is due to the fact that the 

 relationships of the Pyralidina to the Psychina, on the one hand, 

 and to the Butterflies on the other, depend very greatly upon 

 the answer. For, as we have already shown on p. 674, the con- 

 dition of Rs in the Psy china is one in which R 3 has migrated 

 over to R 4+ 5 in the pupal tracheation; and this specialisation 

 has become even more emphasised in the imaginal venation. But, 

 in the Butterflies, the condition of Rs in the pupal tracheation 

 is quite different from this. As we shall show on p. 684, through- 



*The coiu'se of M is sometimes indicated by a faint line or groove, but 

 is never chitinised as a true vein. 



