62 EN TOMOLOGY 
beetle, the folded wing (Fig. 72, B) exhibits a costal joint 
(a), a fold parallel to the transverse vein (b), and a complex 
joint at d. The wing rotates upon the articular head (a/) 
and when folded back beneath the wing-covers the inner 
end of the cotyla (c) is brought into contact with a chitin- 
PIGS 72! 
Wing of Leptinotarsa decemlineata. A, spread; B, folded; a, costal joint; ah, 
articular head; an, anterior system of veins; b, transverse vein; c, cotyla; d, joint; 
m, middle system of veins; p, posterior system of veins.—After Tower. 
ous sclerite of the thorax, which stops the further movement 
of the cotyla medianward, and as the wing swings farther back 
the middle system of veins (7) 1s pushed outward and ante- 
riorly. This motion, combined with the backward movement 
of the wing as a whole, produces the folding of the distal end 
of the wing. There are no traces of muscles or elastic liga- 
ments in the wing which could aid in the folding. 
Mechanics of Flight.—The mechanism of insect flight is 
much less complex than one might anticipate. Indeed, owing 
to the structure of the wing itself, simple up and down move- 
ments are sufficient for the simplest kind of flight. During 
