1660 THE BUTTERFLIES OF NEW ENGLAND. 



hinge at the very crust of the thorax ; the resistance of the air in their 

 beats must be considerable, especially at the extremities of the wings, and 

 all direct appliances for motion nmst be at the extreme base, under a 

 highly disadvantageous leverage. 



A close examination of the structure at the jointage will, however, show 

 that a short arm of the lever does pass within the flexible walls of the sides 

 of the thorax, and that the body wall above is more rigid and removed 

 slightly nearer the centre of the body than the more flexible wall below the 

 wing ; and two sets of vertical muscles will be found attached to this short 

 arm, both, however, side by side on the under surface of the arm ; the 

 inner set, however, is attached within, the outer set without, a point oj)po- 

 site the edge of the wall of the body above the wing. The inner set 

 serves to raise, the outer, which hugs the wall of the body, to lower the 

 wings. 



Now while such an arrangement must, and as experiment shows does, 

 have such an effect, it would seem as if it must work at a decided disad- 

 vantage and be quite inadequate to such rapid and powerful movements as 

 are found in some insects ; in such, to give an example only among butter- 

 flies, as we see in the heavy Ijodied, small winged skippers ; or to give such 

 a powerful rigidity to the wings when the insect is killed by prussic acid as 

 will sometimes cause a wing to break in our endeavor to move it. More- 

 over if we dissect the body of any butterfly, we shall find the entire thorax 

 crammed with muscles wliich have both their attachments on the walls of 

 the thorax itself, one principal set running in an obliquely vertical, another 

 in a longitudraal direction, and whose only possible use can be to flatten 

 or shorten the thorax itself. Why such an apjiaratus to accomplish this? 

 Is it for respiratory purposes, as one may at first surmise? But there are 

 no such muscles, either as regards direction or tremendous power, in the 

 abdomen where most of the respiratory openings occur. Apply experiment 

 again and it is quickly seen that the action of the first set, the obliquely 

 vertical muscles, which flatten the thorax, is to raise, of the other set to 

 lower, the wings. These two entirely different agencies, one acting 

 directly on the wing itself, the other indirectly, by the pressure of the 

 edges of the body walls next the base of the wings, acting in unison, 

 suflice to translate compound action into simple motion. Other special 

 muscles serve for such other movements of the wings as are necessary. 

 This will explain whj' the movements of the opposite wings are simultane- 

 ous and always alisolutely co-ordinated : the more powerful muscles of the 

 thorax cannot act upon the wings of either side independently of the 

 opposite. 



Comparative studies of the muscular appliances for fligiit in difterent 

 buttei'flies have never been undertaken, but they might yield some interest- 

 ing results, for the difference in the character of ffight between most of the 



