BY n. .1. TILLYAKD. 



639 



A[)art from the two t'anulies dealt with in tlie i)recec]iijti- }»ara- 

 giaph, all those listed in the second group have the inacrotiiehia 

 well developed upon the cross-veins. 



Another interesting specialisation in this Order is iJic dt-Nel- 

 opment of .scales, which occur in the family Berothido' Thev 

 occur upon a more or less restricted area of the hind wing, in the 

 females only, of the genus Spermoj^horella (Text-fig. 24), and upon 

 the fringe of the wing in the genus 

 Isoscelipteroit. They are clearly only 

 modified macrotrichia. 



The Archetype of this Order, then, 

 may be defined as having had the 

 archedictyon and its macrotrichia com- 

 pletely eliminated, owing to the unique 

 specialisation of the venation : the 

 macrotrichia, consequently, only oc- 

 curring on the main veins and their 

 branches, but well developed : and the 

 microtrichia also present and of normal 

 size. From this original type, the line 

 of evolution runs forward in the direc- 

 tion of complete elimination of the 

 mici'otrichia, with subsequent invasion 

 of the cross-veins by the macrotrichia, 

 and with the occasional formation of scales (in two cases only). 



Text-tig. 24. 



Order MECOPTEKA. (Text-fig. 25). 



In this (Jrder, microtrichia are always exceedingly well de- 

 veloped all over the wing. Macrotrichia are found upon the 

 main veins and their Ijranches, but never upon the true cross- 

 veins. The archedictyon has been completely eliminated, but its 

 macrotrichia still persist upon the wing-membrane. (Text-fig. 25). 

 OwiniT, however, to the small number of macrotrichia that can 



* Portion of a main vein fioni middle of hindwing of Sptrmojihorefia 

 dUiitminata Till., ? , showing normal macrotrichia interspersed with seed- 

 Hke scales; ( X 90). 



