45 
radius ; while the mode of flight, by quick up-and-down beats, or 
again by a sailing and gliding through the air, could not fail to leave 
some indication in the framework of the wings as to which mode of 
progress was chiefly favoured by the insect. 
Fig. 1—A GENERALISED WING (typical). 
Hind-wing of Hepialus humuli, enlarged. The impression obtained by photo- 
graphy, and with the veins all named and numbered, according to the 
system Redtenbacher-Comstock. Radial nervures = III; Medial nervures 
= IV; Cubital nervures = V. 
A study of the Neuroptera and the more generalised types of 
insects, together with a comparison of /epza/us, shows that in the 
primitive butterflies the fore and hind wings must have been equally 
developed, and placed further apart than we find them to-day. The 
specialisation has proceeded in the direction of a diminution in size 
of the hind thoracic ring, and a consequent bringing of the front and 
hind pair of wings together. It has further continued to progress by 
the greater specialisation of the hind pair over the front pair of wings 
in the neuration of one and the same individual. For in Hepzalus 
the hind-wings have a five-branched radius as well as the fore-wings , 
while almost all other Lepidoptera have the radius three- to five- 
branched on the front wings and only one-branched on the second- 
aries. ‘The only exceptions so far known are the Micropterygides, 
and perhaps also certain Tineids, such as C. fameliella.  ‘There- 
fore, in this main point, the hind-wings are generally the more 
