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PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
The next point to consider is their attachment to 
the thorax. The wings are connected with the thorax 
of the insect by ball and socket, or, as they are 
termed, universal joints ; so that the wing can oscillate 
or twist in any direction, and is capable of every 
variety of motion. If you have ever watched a fly 
dressing its wings, you will know how great is the extent 
to which it can twist them with the anterior margin both 
forwards and upwards, and backwards and downwards. 
The next point to notice is the muscular attachments of 
wings, and upon this I quote from Professor Pettigrew on 
“Animal Locomotion ” :— 
The muscles are arranged in the form of a cross —i e., there is 
a powerful vertical set which runs from above downwards, and 
a powerful antero-posterior set which runs from before back¬ 
wards. There are likewise a few slender muscles which proceed 
in a mere or less oblique direction. The antero-posterior and 
vertical sets of muscles are quite distinct, as are likewise the 
oblique muscles. Portions, however, of the vertical and oblique 
muscles terminate at the root of the wing in jelly-looking points 
which greatly resemble rudimentary tendons, so that I am in¬ 
clined to believe that the vertical and oblique muscles exercise 
a direct influence on the movements of the wing. The shorten¬ 
ing of the antero-posterior set of muscles (indirectly assisted by 
the oblique ones) elevates the dorsum of the thorax by causing 
its anterior extremity to approach its posterior extremity, and 
by causing the thorax to bulge out or expand laterally. This 
change in the thorax necessitates the descent of the wing. The 
shortening of the vertical set (aided by the oblique ones) has a 
precisely opposite effect, and necessitates its ascent. While the 
wing is ascending and descending the oblique muscles cause it 
to rotate on its long axis, the bipartite division of the wing at its 
root, the spiral configuration of the joint, and the arrangement 
of the elastic and other structures which connect the pinion with 
the body, together with the resistance it experiences from the 
air, conferring on it the various angles which characterise the 
down and up strokes. 
Every entomologist is aware of the synchronism or dupli¬ 
cate action existing between the wings thus, if on 
attempting to set a specimen recently killed, the one wing 
is depressed or moved forward, a similar movement (though 
usually in a less degree) takes place with the other wing. 
This is on account of the movement of the dorsum of the 
thorax, which takes place as previously explained by 
Professor Pettigrew. 
Having briefly referred to the construction of the 
wings of insects, we must now come to notice the 
various phases of the wing's action in the perform¬ 
ance of its function as the elevator and propeller of 
the body of the insect. Now, the wing acts upon the air 
as a lever combined with a screw or rotating action. 
During the descent of the wing the body is elevated and 
propelled. At the termination of the down-stroke the body 
falls slightly, and this (aided by the muscles and the action 
of the air) gives the wing an upward impulse ; but as the 
wings of most insects are vibrated so very quickly this fall 
is imperceptible; it is, however, to be clearly seen in those 
insects where the action of the wings is slow, such as the 
common white and brown butterflies. These insects, we 
observe, fly with a zig-zag, up-and-down movement,—the 
body rising and falling with every stroke of the wings, and 
giving them the uncertain and wavering motion so peculiar 
to all insects which vibrate their wings so slowly. I have 
referred to the rapidity of the wing movements of most 
insects ;—let me give you a few particulars on this point, 
for I think it is one of the most wonderful of vital pheno¬ 
mena. Astronomers seem to delight to baffle us by 
rehearsing how many millions of miles separate us 
from some of the fixed stars, but I think we have in the 
vibrations of such an insignificant creature as a fly an 
equally puzzling reflection. Professor Marey, who has 
made elaborate investigations into the number of vibrations 
per second of the wings of various insects, gives the 
following list:—housefly, 330 ; dronefly, 240 ; bee, 190 ; 
wasp, 110; hummiug-bird moth, 72 ; dragonfly, 28 ; white 
butterfly ( Rapce ), 9. If we watch one of these insects 
which vibrate the wings at a high speed, such as the 
housefly or bee, only a blurred impression is left upon the 
retina of the eye;—we cannot by sight observe their move¬ 
ments. If we could only see the root of the wing, we 
might be able to trace the various pulsations; but of course 
a slight movement at the root necessitates a corresponding 
movement at the extremity of the wing, which gains in 
speed according to the length of the pinion, for while the 
root is making a short movement, the tip of the wing has 
in the same period of time to pass over a much more 
extended range, and therefore must be greatly accelerated 
in speed. (Plate I., fig. 2.) Although the numbers that 
have been given may probably be looked upon as correct 
for ordinary flight, yet there is no doubt that these num¬ 
bers can be and often are materially increased under dif¬ 
ferent circumstances. 
Professor Pettigrew gives many cases of insects still 
retaining the power of flight though large portions of their 
wings are detached, and I have myself many times 
repeated some of his experiments;—thus, the blue bottle- 
fly will still retain the power of flight though § of the 
posterior margins of its wings are removed. The dragonfly, 
though it loses either its first or second pair of wings, 
is not disabled, but can pursue its airy flight with 
apparently little difficulty; and the butterfly, though 
robbed of its hind pair of wings, is not altogether 
