MOTION. 
to the cubic contents of the body, endows this 
insect with great powers of suspension in the 
air and with great velocity of motion. The 
triangular figure of the wings prevents the un- 
steady undulating progression observed in the 
diurnal Lepidoptera, and the flight is conse- 
quently more direct as well as more rapid. The 
wings of many of the moths are of considerable 
dimensions. The largest male Atlas moth in 
the collection at the British Museum measures 
5% inches on each side, estimated from their 
axes of motion to the apices of the wings, pre- 
_ senting a total area of 264 square inches. If 
the force of the muscles acting on the wings is 
proportional to their areas, they must possess 
the most extensive power of flight. The Bombyx 
mori, or silk-worm moth, is stated to travel 
more than a hundred miles a day.* 
The Neuroptera have a separate set of 
muscles appropriated to the movements of 
each wing, which being detached can be 
moved either synchronously or independently 
of each other: the muscles also are actually 
inserted into the wing, instead of moving 
them indirectly, as in other orders of insects, 
The surfaces of the four wings of the Libellule, 
or dragon-flies, are nearly equal in most species ; 
they are always expanded in repose, and ex- 
tended horizontally at right angles to the axis 
of the body, so that they take flight in an in- 
stant. Their figure is lanceolated. The ratio 
of the united areas of the four wings to the 
weight of the body is greater than in the Cole- 
optera and Hymenoptera, and the muscular 
power is proportionally augmented. ‘The arti- 
culation of the wings being situated above the 
centre of gravity keeps them steady in flight: 
their velocity is very great, exceeding that of 
the Swallow. Leeuwenhoek once observed one 
of this tribe in a menagerie 200 feet long, 
chased by a swallow ; the insect flew with such 
velocity, and turned to the right and left in all 
directions so instantaneously, that the swallow, 
with all its powers of flight and tact in chasing 
insects, was unable to capture it, the insect 
always keeping about six feet in advance of the 
bird. The great length and surface of the 
wings of the Libellule, and the power of the 
muscles acting on them, is such that they appear 
to be never tired of flying in quest of their prey. 
In a specimen of the Hshna maculatissima, 
____ which weighed fourteen grains, the area of the 
anterior wing was 0.7324 in. the posterior 
0.8988 in. and the area of the four wings 
3.26408 square inches. The preponderance of 
surface in the posterior wing enables the Libel- 
lulz to change the direction of their path of 
Motion with great facility, and to capture their 
prey on the wing. «Previously to taking flight, 
this Ashna exerts a vibratory movement with 
its wings; the oscillations are made in very 
minute ares, and with great rapidity, producing 
a faint though distinct sound. The pitch indi- 
cates that the wings perform ninety-six vibrations 
inasecond. On taking flight the wings oscil- 
late through larger arcs, with a less number of 
vibrations, the amount of which it is not easy 
* Lin. Trans. vol. iii. p. 40. 
423 
to determine, and does not depend, as some 
distinguished entomologists have supposed, on 
their mutual friction. 
In a Triphena pronuba, weighing 8.545 
grains, the area of the anterior wings measured 
0.6213, and that of the under wings 0.68 
square inches, making the sum of the areas of 
the four wings 2.6026 square inches. 
In the Hymenoptera the ratio of the areas 
of the four wings to the weight of the 
insect is less than in the Neuroptera, and 
they are consequently obliged to make a 
greater number of strokes in the same inter- 
val of time in order to suspend themselves 
in the aig. The areas of the upper are greater 
than those of the under wings. When ex- 
panded they are retained in the same place, 
and are linked together by means of small 
hooks, so that the upper and under wings act 
simultaneously and with greater power. A 
humble bee, which weighed 6.2 grains, had 
wings the sum of whose areas measured 0.366 
of a square inch, or rather more than sth of a 
square inch to each grain weight of the body. 
Bees are not only celebrated for the geo- 
metry displayed in the structure of their cells, 
but also for the precision with which they re- 
turn to their homes by the shortest path or in a 
straight line. The collectors of honey make 
use of this fact to discover their nests. Having 
captured two of these insects, they separate 
them some yards from each other, and on setting 
them free, ascertain with an instrument the 
angles respectively made by the lines of their 
flight with that between the points of their de- 
parture, then the point where the two lines of 
direction intersect each other indicates the posi- 
tion of the nest. The humble bee, wasp, and 
hornet fly with great force, but owing to the 
weight of their bodies, compared with the areas 
of their wings, cannot fly with much speed 
against a strong wind, so that a person might 
easily outstrip them by running in the same 
direction against the wind. When disturbed, or 
before leaving their abode, they wheel round the 
spot in a large circle, and then fly off at a tangent 
to some part of the curve. The Ichneumons are 
provided with a far greater expansion of wing, 
In proportion to their weight, than the Bees, 
and can consequently sustain themselves in the 
air with less expenditure of muscular action. 
In a species of ichneumon allied to Ophion 
luteus, which weighed 0.5 gr. the areas of the 
anterior wing measured 0.0832 in. the poste- 
rior 0.0480 in. the sum of the two wings 
0.1322 in. and that of the four = 0.2644 in. 
The Diptera are furnished with only two 
wings, which when in repose lie directed 
obliquely backwards upon the abdomen; their 
figure is nearly that of an ellipse, and their 
areas are ample when compared to the weight 
of their bodies. Three examples of Musce vo- 
mitoria for instance were found to weigh 2.4375 
grains, which gives for the mean weight of each 
0.8025 gr. and the mean areas of both wings 
were found to be from 7th to Ath of a square 
inch. Instead of posterior wings they have 
poisers, the articulation of which to the thorax 
is placed more posteriorly than in the four- 
