BY R. J. TILLYARD. 



581 



in Xyleutes (Text-fig. 85), and the intervening space will still 

 become ehitinised in the imaginal venation, thus completing the 

 formation. I have not succeeded in finding the interanal cross- 

 vein /«! in any pupa of this Suborder; unless, indeed, the forma- 



Text-Fig.54. 

 Evolution of the secondary anal Y-vein in the hindwings of the Lepido- 

 ptera Heteroneura. a, original Homoneurous condition; b, con- 

 dition in pupal wing of Xyleutes (fam. Cossidae) ; c, condition in 

 pupal wing of Carpocapsa (fam. Tortricidae) ; d, condition in 

 imaginal wings of the Tortricina ; e, stage in which the upper arm 

 of the Y-vein (1A) is degrading ; f, the final stage, in which 2A is 

 left as a straight, simple vein, as in the Butterflies. Lettering as 

 on p. 535. 



tion just mentioned in Xyleutes indicates that the tracheal out- 

 growth from 1A proceeds along the channel of that cross-vein. 

 (2) In the hindwings of the older Lepidoptera Heteroneura 

 only, but nowhere else amongst the Orders of the Complex, there 

 is present a remarkable specialisation in the form of an anal 

 Y-vein secondarily formed, as the result of the curve given to 

 ] A by the older formation known as the eubito-anal Y-vein, 



