LEPIDOPTERA. 



201 



In the flight of insects it is important that the two wings of each 

 side should act together, and we find that this is secured in most 

 orders by uniting them in some way. In the Lepidoptera two dis- 

 tinct methods are employed ; in some it is done by means of & jugum, 

 in others by means of a frenulum or its substitute. As neither the 

 jugum nor the frenulum could be derived from the other, we infer 

 that the primitive Lepidoptera possessed neither of these organs, but 

 had wings that were quite distinct from each other. In the course of 

 time there was developed in some of the descendants of these primi- 

 tive forms a jugum ; while in others there was developed a frenulum. 

 Of course in each case the development was a gradual one, extending 

 through many generations. Thus the frenulum at first was probably 

 merely a bunch of hairs like 

 those elsewhere on the wings; 

 but these became stiffer and 

 stiffer in succeeding genera- 

 tions. 



The descendants of those 

 ancient Lepidoptera in which a 

 jugum was developed constitute 

 the suborder Jugatce ; while the 

 descendants of those in which 

 a frenulum was developed con- 

 stitute the suborder Frenatce. 



We know but little of the 

 Jugatae, as nearly all of them 

 have perished. There remain 

 only two small families, the 

 Hepialidae and the Microptery- 

 gidae. But these families are 

 very widely separated, and hence 

 it is safe to assume that they are 

 the remnants of what was in 

 past times a large fauna. 



In the Frenatae, however, 

 there exist to-day many families, 

 each exhibiting its own methods of specialization. 



In some of these families the frenulum has been preserved and 

 perfected to a greater or less extent. But in others a curious change 

 has taken place. 



It is obvious that if the two wings of each side overlap to a great 

 extent, their acting together will be assured by this fact. And this is 



Fig. 241. — Wings of Ancea andria. 



