the coxe to the trunk is by cotyloid joints, 
as in the Rhimophore, or by ginglymoid 
joints, as in the Lamellicornes; and between 
the trochanter and femur, the coxa and tro- 
_ chanter, the femur and tibia, the joints are 
usually ginglymoid : the axis of each of these 
joints is turned at right angles to the next, 
_ so that, as Dr. Roget remarks,* “ there results 
from the combination of both, a capability in 
the thigh of executing a circular motion, in a 
_ manner almost as perfect as if it had revolved 
‘in a spherical socket. The principle of this 
_ compound motion is the same as that employed 
_ on ship-board for the mariner’s compass and 
other instruments which require to be kept 
_ Steady during the motion of the ship. For this 
_ purpose, what are called gimbals are used, the 
_ parts of which have two axes of rotation at 
tight angles to each other, so as to enable the 
mpass to take its proper horizontal position, 
matever may be the inclination of the ship.” 
le remaining joints of the legs of insects are 
also ginglymoid. The tarsi, which vary in 
‘number from two to six, terminate by a double 
_ hook; those on the anterior pair of legs are 
_ directed backwards; those on the middle pair 
_ inwards ; and those on the tail-piece, forwards ; 
_ bywhich disposition the insect is enabled to 
"Tay hold of rough surfaces, and to walk up in- 
_ clined or vertical planes with security. 
' _In the progression of insects, the fore and 
middle legs are extended, and the hind legs 
flexed previously to urging the body forwards ; 
‘in doing which, the actions of these legs are 
_ feversed. The simple hook terminating the 
_ locomotive organs of most insects will not en- 
_ able them to walk on water, to climb vertically 
On glass, or stand inverted on ceilings, actions 
_ which many can perform, and for this purpose 
_ 4n additional apparatus is therefore provided. 
_ The common Gnat and some Coleoptera 
Which walk on the surface of water, have 
the tarsi furnished with a brush of fine hairs, 
_ which appear, when the surfaces are free from 
Moisture, to repel the fluid with sufficient 
_ force to sustain the weight of the animal, and 
in confirmation of this theory, it is found that 
if the legs are moistened with spirit of wine, 
he animal immediately sinks and is drowned. 
Ose insects which ascend vertically on the 
_ Surface of glass, or remain suspended in an 
& __ inverted position from the ceiling, are furnished 
with an additional apparatus. We have a 
familiar example in the House-fly, which has 
_ the extremities of its feet furnished with two 
_ funnel-shaped membranous suckers, moveable 
____ by muscles in every direction, by which they 
are capable of exhausting the air on very 
_ Smooth surfaces, thus causing the pressure of 
the atmosphere to sustain the weight of the 
___ body : the area of these suckers is so beautifully 
adjusted to the weight of the insect, that the 
__ pressure of the air alone is more than sufficient 
to sustain the weight of the insect without ex- 
___ értion, and to suspend its body to a ceiling in 
an inverted position. The centre of gravity is 
__ 4s thus suspended, instead of being supported, 
* Bridgewater Treatise, i. 294, 
MOTION. 
443 
the legs having merely to resist the force of 
gravity upon the body. In the Bluebottle-fly 
( Musca Vomitoria ) these suckers are conspi- 
cuous, and the edges being serrated enable 
them to apply the disc of this pneumatic 
apparatus to any kind of surface, 
Fig. 237. 
In the 
Fig. 236. 
Bibio febrilis (fig. 236), the foot is furnished 
with three suckers, in the Musca domestica 
with two (fig. 237), and in the Cymbex 
Lutea with five. Numerous other species, 
amongst which is the common Wasp, are fur- 
nished with cushions and analogous suckers, 
which enable them to ascend vertically on 
glass. 
The predaceous insects run with great velo- 
city in proportion to their height. Those which 
are furnished with very short legs must ad- 
vance them at intervals of time corresponding 
to the square roots of their length, on the 
supposition that their legs are subject to the 
same physical laws as those of the human 
race. Mr. Delisle observed a minute fly run 
three inches in half a second, making 540 
steps in the same time ; each of these steps 
0.0056 
of an inch in length. The great number of 
steps taken by these minute animals conveys 
to the mind of the observer an impression 
that the animal is running, whereas it is merely 
walking, the body not swinging freely in the 
air, as is necessary, according to the definition 
of Weber, to constitute the act of running. 
Myriapoda.—In the Myriapods, the great 
number of legs and the celerity of their move- 
ments, as for example, in the Scolopendra, 
render it difficult to detect the order of their 
motions. The numerous segments entering into 
the lengthened form of the trunk, each of 
which is furnished with a pair of legs, give to 
the body great flexibility, and enable the 
Myriapods to turn from a right line to any 
curved or angular path, or to pass over rough 
surfaces with facility. The legs, in number from 
fourteen to forty-two, are short, and directed 
laterally ; they are composed of four segments ; 
all the joints, except that by which they are 
attached to the trunk, are ginglymoid, and 
terminate in a sharp conical claw, which gives 
precision and security in climbing. The legs 
appear to move in a determinate order; every 
3 
t have been consequently —— 
mus q y Pats 
