ANATOMY AND PHYSIOLOGY. 123 
wards and forwards. And I quite accept his con- 
clusion as correct. Apart from various other con- 
siderations, which it would occupy too much space 
to discuss here, one very strong reason against the 
commonly received opinion of the wings strikng 
backwards, is that the wings do not move easily in 
that direction. We may learn somethmg from a 
recently killed hornet. If we press the thorax alter- 
nately in the direction in which it would be drawn 
under the influence of the muscles of flight, the 
wings strike downwards and forwards. In the large 
water-scorpion the direction of the movement is very 
obvious: for here the strength of the parts makes 
the direction which the wings take when coupled, 
and from which they cannot be made to deviate 
except by force, quite distinct. The coupled wings 
cannot strike downwards and backwards. Again, 
where the wings are free, as in butterflies and dragon- 
flies, the change from the position of rest to that of 
extreme extension is still downwards and forwards. 
Not to prolong this inquiry there is yet one other 
point for “consideration. Mr. Wenham thinks that 
the amount of muscular force requisite to raise and 
maintain a heavy body in the air is not as great as 
is usually supposed, but after all allowances made, it 
is still very considerable. For, if we are to judge of 
the work to be done by the means which are pro- 
vided to do it with, we can come to no other con- 
clusion than that half the secret of the flight of 
insects lies in the enormous and untiring muscular 
power which is stowed away in their thorax. The 
strong, rapid action of their muscles is to be mea- 
