252 The American Naturalist. [March, 
deed, is it necessary to believe that these branches have been 
long ones, for, as I have elsewhere shown", the specialization 
of scales can come about very rapidly. 
It seems probable that the stem- form of the Lepidoptera 
possessed a wing-clothing much like that now exhibited by the 
Trichoptera, and that the Jugate branched off before the cov- 
ering of fine hairs had been lost, although the tendency of 
specialization had already become manifest. The phylogen- 
etic position of the Jugate, indicated by their wing-clothing, 
quite corresponds with that indicated by the wing venation as 
shown by Professor Comstock. 
Another characteristic of the Jugate, not so distinctly avail- 
able as a recognition character, but of considerable phylogen- 
etic significance, is presented by the structure of the thorax. 
The thoracic structure of the common, wingless, racial form 
of the Hexapoda is probably pretty fairly shown by the living 
Campodeas. With the appearance of wings the musculature of 
the two hinder segments of the thorax was necessarily largely 
increased, and those segments increased in size and strength. 
The chitinous exoskeleton became especially firm and strong 
for the attachment of the muscles, and the two segments ac- 
quired a bulk and form proportional to the extra development 
of the musculature. In the more generalized of winged insects 
the two pairs of wings are subequal in size and importance, 
and are quite independent of each other. Correspondingly, 
the meso- and metathoracic segments are subequal in size 
and form. The Paleodictyoptera of Scudder, including all the 
Paleozoic insects, are credited by him with the following char- 
acters (among others): “ thoracic segments subequally devel- 
oped; both wings closely similar in shape and with a simple 
neuration.” The condition of wings and thorax in many of 
the living generalized neuropteroid insects well illustrates this 
state. (See fig. 1, plate X VII.) 
But the parachute-like function which these broad sub- 
equal wings subserved began to give way to a more effective 
aerial locomotion. A tying together of the fore and hind 
wings of each side to secure synchronous action, and a 
ê See paper on scales referred to. 
