56 ENTOMOLOGY 
Among adult insects, female scale insects are exceptional in 
being legless. . 
Walking.—An adult insect, when walking, normally uses 
its legs in two sets of three each; thus the front and hind legs 
of one side and the middle leg of the other move forward 
almost simultaneously—though not quite, for the front leg 
moves a little before the middle one, 
which, in turn, precedes the hind leg. 
A..adc During these movements the body is sup- 
ported by the other three legs, as on a 
tripod. The front leg, having been ex- 
tended and its claws fixed, pulls the body 
forward by means of the contraction of 
the tibial flexors; the hind leg, on the 
contrary, pushes the body, by the short- 
ening of the tibial extensors, against the 
resistance afforded by the tibial spurs; the 
canes -fta middle leg acts much like the hind one, 
but helps mainly to steady the body. 
Different species show different peculiari- 
ties of gait. In its analysis, the walking 
of an insect is rather intricate, as Graber 
and Marey have shown. 
The mode of action of the principal 
Lee es ae leg muscles may be gathered from Fig. 
terior aspect. abc, ab 65. Here the flexion of the tibia would 
ductor of coxa; adc, 
adductor of coxa; ef, 
extensor of femur; et, line s 7; and the backward movement ot 
extensor of tibia; ff, 
flexor of femur; ft, the leg due to the upper coxal rotator 7 
fexor of tibia}. 1% would cause the spur to follow the are 5 3. 
flexor of tarsus; rt, re- v 
tractor of tarsus.—After As the resultant of both these movements, 
MIALL and Denny. 
cause the tibial spur (s) to describe the 
the path actually described by the tibial 
spur is s 2; then, as the leg moves forward, the curve is con- 
tinued into a loop. 
Caterpillars use their legs successively in pairs, and when 
the pairs of legs are few and widely separated, as in Geomet- 
ride, a curious looping gait results. 
