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, Tenthredinid?e) 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 tootlied 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 



