BY R. J. TILLYARD. 



Gti3 



dently closely analogous to the single anal loop or Y-vein of the 

 forewings. It is, however, important to notice that, in the 

 forewing, 1A is the dominant member of the Y-vein, while 2A is 

 reduced. In the hindwing, the reverse is the case. The im- 

 portance of this formation lies in the fact that it occurs through- 

 out the Superfamily Tortricina, and thus affords a striking proof 

 of the very direct descent of that group from the base of the 



Text-Fig.88. 



Venation of hindwing of Xyleutes eucalypti (Scott) . (x 0-8) . Lettering 

 as on p. 535. 



Cossid stem. This small basal Y-vein is also to be seen in a 

 few Tineina {Taleporia, Adela, Wingia, Acompsia), in the 

 Castniidae and Thyrididae, but is eliminated in the majority 

 of the Tineina and Pyralidina, as well as from all the Psychina 

 and the Butterflies. 



At metamorphosis, there is a great increase in the calibre of 

 the veins at the base of the wing. The basal formations, such 

 as M 5 , the approach of 1A to Cu' 2 , and the fusion of 1A with 

 2A, become withdrawn very close to the actual wing-base, and 

 partially lost in the copious deposition of vein-chitin there laid 

 down. An examination of the underside of a carefully de- 

 scaled wing is necessary to reveal their presence. It will be 

 seen that, in most Heteroneura, the presence of these archaic 

 formations becomes more and more masked as specialisation 

 proceeds, until they become practically obliterated in the higher 

 groups, first in the hindwing, in which they are never so con- 

 spicuously developed as in the fore, and then in the latter also. 



