ANATOMY AND PHYSIOLOGY. 121 
the smoothness of flight. The dragon-fly, the swallow 
of insects, may seem to constitute an exception to 
this rule, as her wings do not lock. But the cases 
are not strictly comparable, as she has an exceptional 
power of altering the direction of her wings, in con- 
nection with the unusual mode of the insertion 
of her muscles of flight. Having already spoken 
of these, I would only remark further here, that 
there is something so peculiar in the flight of the 
dragon-fly as might lead one to predict, even without 
anatomical demonstration, the existence of some 
peculiar structural arrangement of her wings. If 
we watch her over a pond we see how she stops 
suddenly in the most rapid dashes, and, for all her 
strength of wing, seems to have more frequent need 
of rest than most other insects. And, rapid as her 
flight is, she is readily caught by a quick hand, as 
she comes staring and rustling in our faces. 
The action of the wings is most easily observed 
when they are separated. As the pretty Syrphus 
hovers over a flower, the position of the elliptical 
figure which her wing describes shows that the 
vertical extent of movement is greater than the 
horizontal; indeed it must be so, or else she would 
advance. By the same mode of reasoning it is clear 
that the downward blow must be stronger than the 
upward; the wing must be feathered on the return 
stroke, or else she would fall. So, when the wasp 
poises herself, she unlocks the wings, and all forward 
motion is at once stayed. I have often seen this, in 
the window-case where all my working wasps’ nests 
are placed. The unlocking of the wings seems as 
necessary a preliminary to the landing of a wasp, as 
