BY R. J. TILLYARD. 



6(il 



separate throughout their lengths. In - the corresponding 

 imaginal wing, the radial cell or aerole (re) becomes closed 

 distally by a slight fusion of R^+5 with R :? (Text-fig. 86) . The 

 original method of fusion of this cell, by means of the cross- 

 vein ir (absent in Xyleutes) is still to be seen in the more ar- 

 chaic Cossid genus Macrocyttara (Turner, 32, p. 169, fig. 22), 

 but this genus has R.2+3 and R i+ 5 arising more widely apart 

 from R x than in Xyleutes. 



The vein M 5 appears early in the pupal wing of Xyleutes, 

 and a trachea of great strength grows out into it either in late 

 pupal life or at metamorphosis. In the imago, this vein re- 

 mains primitive, in so far as it is not completely aligned with 

 Cii! ; it also becomes of immense size in comparison with the 

 weak main stem of Cu below it (Text-fig. 86). Cu 2 remains 

 a complete vein, though not strongly formed; and the small basal 

 piece of Cuj is clearly to be seen as a fairly strong vein. 



In one pupa which I dissected, a very definite trachea M 4 

 was found in both wings. This formation is figured and dis- 

 cussed more fully in Section vi., p. 586. The other changes in 

 the regions of M, Cu and the anal veins can be easily gathered 

 by comparing Text-figs. 85 and 86. 



The pupal hindwing of Xyleutes (Text-fig. 87) differs, of 



Text-Fig.87. 

 Tracheation of a, hindwing of freshly formed pupa of Xyleutes eucalypti 

 (Scott), (x 3-3) ; b, tracheation in the region of the discocellulars, 

 in a more advanced pupa. Lettering as on p. 535. 



