G46 THE PANORPOID COMPLEX, ii., 



somewlmt smaller in size than those upon the veins. This differ- 

 ence is also to be seen, somewhat more intensified, in the oldei- 

 types of Trichoptera, as may be seen in' the figure taken from 

 lihyacophihi dor^<ilis (Text fig. 30). Not only are the macrotrichia 

 of the veins larger, but they remain for the most part straight 

 and stifi:', whereas those of the membrane (derived originally from 

 the arched ictyon), are slenderer, and inclined to be slighth^ 

 curved. 



A single line of evoluti(m maybe said to characterise the whole 

 Order. It consists in the gradual greater and greater prolifera- 

 tion of the macrotrichia of the membrane, togethei' with various 

 specialisations of the macrotrichia upon the veins. Thus there 

 is produced that excessively hairy type of wing that is especially 

 associated with this Order. In many genera, the stiff bristles of 

 the veins become reduced, either in part, or altogether, to the 

 same type of slender flexible hairs that we find upon the mem- 

 brane; in others, certain sets of hairs, especially at the base of 

 the cubitus, become erect and bristly. In the Hydroptilid(€, all 

 the macrotrichia of the forewings become erect and thickened, 

 while the hindwing develops an exceedingly long fringe. 



h 



Text-lig.81. 

 Forms of scales found in Trichoptera : n, a narrow, lanceolate scale, with 

 sini^le longitixdinal stria, from wing of an unnamed Leptocerid 

 (Broken Hill, X.S.W.); ( x350): h, a lanceolate scale with three 

 longitudinal striie from wing of Plectrofarsns (jravenhori^ti Kol. ; 

 ( X 400). 



The slender, flexible macrotrichia of the membrane found in 

 the wings of Trichoptera are exactly comparable with those of 

 the PsijckodidcH in the Order Diptera (Text-fig. 27). Like them, 

 thev are easily converted into elongated lanceolate scales. The 

 simplest type of such a scale is one in which the flattening pro- 

 duces only suflicicnt width to allow of the development of a single 



