Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/429/
MOTION. 421 
strokes made by the wings of insects as well as 
of birds during flight, it is necessary to take into 
the account the length of the arc in which they 
oscillate. 
The oscillations of the wings of insects are 
too rapid to be numbered by common observa¬ 
tion. The principles of optics,* acoustics, and 
dynamics have been employed to determine 
them during their flight. According to Bur- 
meister the pitch of the sound made during 
flight varies with the number of strokes made 
by the wings, although the production of the 
sound is perfectly independent of them.f If 
the number of strokes is synchronous with 
the number of vibrations which produce the 
sound, we can ascertain the number of their 
oscillations very readily; but we are not yet 
furnished with sufficient evidence that each 
stroke of the wing is coincident with one 
musical semi-vibration to determine this ques¬ 
tion with precision. According to the analysis 
made on the flight of birds, if the same data 
may be considered applicable, we shall see by 
Chabrier’s investigations when all other things 
remain the same, that the number of strokes 
made by the wings of insects will vary as the 
square roots of the weight directly, and of the 
area of the wings inversely. 
In the Coleoptera, the ratio of the area of the 
wings to the weight of the insect is small in 
comparison with other orders. The elytra of 
the Coleoptern add to their weight and surface 
in passing through the air, without contributing 
either to the vertical elevation or horizontal 
velocity of the insect; on the contrary, as their 
surfaces are inclined to the axis of the body 
and the direction of motion, they retard the 
velocity of the beetle in moving against the 
wind. The centre of the forces lies posterior 
to the articulation of the wings, and as the 
angle of inclination of the elytra tends to ele¬ 
vate the head and depress the abdomen by its 
resistance to the wind, the axis of the body 
becomes inclined vertically during flight. In 
a stag beetle weighing forty grains, the area of 
each elytra measured 0.366364 of a square 
inch, and the true wings, calculated as the 
quarter of an ellipse, gave 0.6263565 of a 
square inch each, or 1.2527126in. for both. The 
same measured by a graduated scale gave 
0.62240 in. each, which shows how nearly the 
form of the true wings approaches to a segment 
of perfect ellipse. Those Coleoptera in which 
the ratio of the surface of the wings is very small 
cannot fly against a strong wind. Olivier says, 
“ None of this class can fly in opposition to the 
wind,’7 but this assertion is opposed by Kirby, 
who states that the Melolonthæ Hopliæ fly in all 
directions; others, as the Cicindelæ, take short 
flights, and may be easily marked down by 
the entomologist. The Cetoniæ expand their 
wings in flight without elevating their elytra, as 
is done by other Coleoptera. 
The Dermaplera, though generally on their 
legs, take flight towards evening. The wings 
* See Nicholson’s Journal, 4to. vol. iii. p. 38. 
t Remarks on the causes of sound produced by 
insects in flying, by Dr. H. Burmeister. Taylor’s 
Scientific Memoirs, vol. i. p. 378, 1837. 
of the earwigs are ample ; the nervures radiate 
from a common centre to the external margin 
of the wings, which they expand like a fan. 
According to Kay, the tegmina of the Orthop- 
tera assist the wings in flight. The Grillus 
domesticus flies with an undulatory motion 
like the woodpecker, alternately making a few 
strokes with the wings in order to give a pro¬ 
jectile velocity to the body upwards, and then 
folding the wings to descend on the opposite 
side of the vertex of a parabolic curve. Owing 
to the analogous structure of their wings, the 
Gryllus campestris and Gryllotalpa are capa¬ 
ble of using them in a similar manner. The 
Hemiptera employ their hemi-elytra to assist 
the wings in flying.* By this means the area 
of the wing is increased, a greater surface is 
given to it for striking the air, the ratio of the 
surface of the wings to the weight of the body 
is augmented, the quantity of action and the 
number of vibrations necessary to sustain it in 
the air is diminished, and the power of flight 
is consequently increased. 
The Lepidoptera are furnished with a far 
greater area of wing in proportion to the weight 
of their bodies than is observed in any other 
flying animal. The under wing approaches in 
figure to the quadrant of a circle, and in many 
species the two meet posteriorly and form a 
semicircle. The anterior and under wings are 
locked together during their descent so as to 
give them a synchronous action, and a compact 
surface to resist the air. The surfaces of the 
two wings on each side increase with the 
distances of their sections from the axes of 
motion ; in the Morpho automedon (fig. 220), 
in which the areas of the sections of the wings 
lying between the parallels 1, 2, 3, 4, drawn at 
equal distances from the axis of the body, will 
be seen to increase (the last one excepted) as 
the distances from the centre of motion of the 
wings increase ; the effect of which is, to throw 
the centre of resistance to a greater distance 
from the axis of motion, so that the muscles of 
the wing act at a mechanical disadvantage ; 
and the weight of the body being small in 
proportion to the area of the wing, the 
body oscillates considerably at each elevation 
and depression, and its flight is rendered un¬ 
steady. 
The surface of the anterior wing is less than 
that of the posterior, being as 2.08 : 2.4483471 
square inches, and the sum of the surfaces of 
the four wings is =9.0566942 inches. As the 
solid contents of the body are very small when 
compared to the surface of the wings, we 
naturally conclude that the Morpho has pro¬ 
longed powers of suspension. The great mag¬ 
nitude of the wings of the Lepidoptera are 
generally in proportion to the weight of their 
bodies, and the force of their muscular system 
endows them with great powers of flight; but 
it is most frequently accomplished in a zig-zag 
path. In the Pontia brassicæ the weight of 
the insect is found to be 1.525 gr. ; the area 
of the anterior wing 0 6 square inch, the area 
* See Dr. Roget’s Bridgewater Treatise, third 
edition, vol. i. p. 313.
        

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