BY R. J. TILLYARD. 



643 



all the main veins and their branches. Here and there these 

 hairs are seen to be slightly flattened out, forming delicate and 

 narrowly lanceolate scales. The culmination of this same line of 



Text-fig. 27. 

 Two portions of a single main vein from the wing of Psi/choda sp., 

 (Hornsby, N.S.W.), to show the triehiation. On the left, normal 

 maei'otrichia, one or two slightly flattened: on the right (distal end 

 of vein), narrow lanceolate scales; { x 875), 



evolution is to be found in the Ciilicidce (Text-fig. 28), in which 

 all the macrotrichia, even those along the wing-border, have 

 become scales; and these scales, in most cases, are of broad form 

 and specialised sculpture. 



Along the second line of evolution, which has been followed 

 by many families of Nemocera, and also by the whole series of 

 the Brachycera and Cyclorrhapha, we can follow out the gradual 

 elimination of the macrotrichia, through such forms as the 

 Tah(iuid<p, where they are still present in large numbers on the 

 more anterior veins of the wing, to the higher Cyclori'hapha, 

 wliei-e they finally cease to exist anywhere except upon tlie costal 

 border of the wing. Text-fig. 29 shows the type of short, stifle* 

 seta into which the macrotrichia develop in this line of evolution. 

 It should be noticed, also, that, concurrent]}' with the broadening 

 and strengthening of certain veins, the macrotrichia upon them 



