BY R. J. TILLYARD. 



589 



with Cuj The genera in which vein M 4 is most frequently 

 strongly chitinised are also those genera in which trachea M4 

 is most frequently present in the imaginal wing, viz. Perissectis, 

 Trictena and Pielus. No pupae of any of these three genera 

 have yet been obtained ; but I shall continue to make every effort 

 to get them, in the hope that trachea M 4 may appear in the 

 pupal wing. 



Taking into consideration the above evidence, coupled with 

 the very evident examples of incomplete fusion in Sthenopis 

 and the fossil Archipanorpa, we are, I think, justified in a belief 



Text-Fig. 59. 

 Evolution of the basal cell and areole in Lepidoptera. a, original con- 

 dition, as in Trichoptera (and in Hepialidae, except for loss of ir); 



b, change to the Hetercneurous condition, as in forewing of some 

 Cossidae (note the approach of the forking of R2+3 towards rf') ; 



c, formation of the open basal cell (be) by abortion of Mi_4 and its 

 branches, as far as im , as in most Heteroneura ; d , formation of an 

 areoeel (ael), by fusion of the areole (re) with the basal cell, 

 through abortion of the chorda (B4-1-5) as in Tortricina, etc. e-g, 

 stages in^,he evolution of the areole (re) ; e, the Homoneurous con- 

 dition (ir absent in Hepialidae) ; f, the Heteroneurous condition, 

 with the forking of B2+3 approaching closer to rf than does that 

 of R4+5; g, closure of the areole by fusion of R3 with R4+5, after 

 loss of ir. Lettering as on p. 535. 



