INTRODUCTION. 
11 
(hip), which is generally large and flat. The second 
joint is called the trochanter , a small joint which some¬ 
times (as in the saw-flies, Tenthredinidm) consists of two 
pieces; next comes the femur (thigh), the largest and 
thickest joint usually of an insect’s leg, then comes the 
tibia (shank), about as long as the femur but not so 
thick, and lastly the tarsus , which consists of a series 
of small joints, varying in number from one to five 
terminating in a claw, often prettily toothed and ac¬ 
companied by a pair of soft velvety cushion-like bodies, 
called pulvilli , very distinct in the house-fly. By 
means of these foot-pads the fly is able to walk on 
perfectly smooth surfaces in a reversed position. All 
sorts of opinions as to how the insect is able to main¬ 
tain such a position, contrary to the laws of gravity, 
have been held ; as that it was owing to the exhaustion 
of air from the foot-pads ; or that the minute hairs, 
which clothe them, aided by the claws, take hold of 
small irregularities of the surface, and thus enable the 
possessor to retain an inverted position. According to 
Mr. Lowne, the last four tarsal joints are occupied by a 
sac, which secretes a viscid fluid, which flows into the 
pad and fills its cavity as well as the hollow hairs with 
which its under surface is covered. The footprints left 
upon glass by flies consist of small rows of dots corres¬ 
ponding to these hairs. 
Of course there are all sorts of modifications, both in 
the legs and their component parts, according to the 
habits of insects; in the leaping insects, as grasshoppers, 
locusts, etc., the hinder pair of legs are much longer 
than the other two pairs, and the thigh or femur is 
very thick and powerful. Insects which swim in the 
