50 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



which order, on the whole, is the more primitive group with a 

 much more complicated venation in its more generalized genera. 



The possession of additional veins in the hind-wings is the most 

 important character which distinguishes the Micropterygidse 

 and the Hepialidse, the other primitive group of Lepidoptera, 

 from all the rest of the Lepidoptera.. Another distinguishing 

 character of these two families, the mode of interlocking the 

 wings was independently pointed out by Spuler and Comstock. 

 The lobe at the base of the fore-wing, which serves to hold the 

 hind-wing in place, the clavus or jugum, is undoubtedly a good 

 primitive character. It is found in both fore- and hind-wings in 

 all the Trichoptera; it also persists though less developed in the 

 hind-wing of the Micropterygidse and is analogous with the pos- 

 terior lobe in the hind-wings of the Diptera. 



Besides the jugum, there are already, in the Micropterygidae, 

 a series of small stiff spines on the costal edge of the hind-wing 

 which assist in holding the wings together. These spines develop 

 gradually in the higher Lepidoptera into the so-called frenulum, 

 which in the primitive group, Aculeate, persist as a series of spines 

 but in the higher groups is reduced to a single strong spine in the 

 male, and to two, three or four similar, w r eaker spines in the fe- 

 males. This is one of the curious examples of how the males 

 lead in the evolution. Another, even more remarkable example 

 of this is found in certain isolated genera w r here the males are 

 ahead of the females in the venation, having two veins entirely 

 coincident, which in the more conservative females are only stalked. 



The ^Egeridse is the only family in which the females have also 

 advanced to the single frenulum. Everywhere else this is dis- 

 tinctly a male character and is a dependable one on which to dis- 

 tinguish the two sexes. 



In some of the highest groups of Lepidoptera, the Saturnids 

 and the Butterflies, where the strongly developed dorsal part of 

 the fore- wings broadly overlaps the equally developed costal 

 part of the hind-wings and thus insures the interlocking of the 

 wings, the frenulum has become obsolete. 



When a partially denuded wing of a Micropterygid is examined 

 under strong magnification it is found that its surface is covered 

 with minute curved spines between the scales and much more 

 numerous than these. Spuler was the first to point out this 

 character, which is found in all Trichoptera, as well as in some other 

 groups such as the Blattidse and the Perlidse. 



These spines, "aculei," are not loosely inserted in pockets in 

 the surface of the wing as are the scales, but are minute, hollow 

 protuberances of the wing itself, and do not rub off when the 

 wing is denuded. This primitive character is lost in all the higher 



