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 a 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 stiller and 
stiffer in succeeding genera¬ 
tions. 
The descendants of those 
ancient Lepidoptera in which a 
jugum was developed constitute 
the suborder Jug at a ; 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 
