MOVEMENT 53 



curved claws, which can be flexed by the tendon of the 

 flexor tarsi muscle, and are of use in affording the insect a 

 hold on rough surfaces. In the act of walking all these 

 various muscles in the creature's six legs are brought 

 into play, the contractions synchronising or alternating 

 rhythmically so as to bring about the orderly movement 

 of the legs in two sets of three as already mentioned 



Besides walking and running, many insects have other 

 modes of movement by means of their legs, such as leaping, 

 gUding, or swimming. In a grasshopper the hindmost legs 

 are by far the longest and strongest of the three pairs. When 

 such an insect is at rest these limbs are seen to be strongly 

 flexed at the knee joint ; the sudden extension of the shin, 

 brought about by contraction of the large muscles within 

 the swollen thighs, propels the insect for a distance of 

 several feet through the air. Fleas are notorious for their 

 power of leaping ; in their legs the haunches are exceptionally 

 long as well as stout, and the flea's jump is due to the extension 

 of the thighs. Aquatic insects such as water-beetles which 

 swim and dive have either the intermediate or hind legs or 

 both pairs flattened so as to serve as oars or paddles. The 

 thighs move on the haunches and there is little change in the 

 relative position of thigh and shin, as the strong limbs are 

 swept rhythmically forwards and backwards. It is note- 

 worthy that in these jumping and swimming actions the 

 two legs of a pair move together, not alternately as in a 

 walk or run. 



By means of suitably arranged muscles many parts of 

 the trunk can be moved in relation to one another. The 

 dorsal sclerites (terga) of the abdomen are Knked up by 

 longitudinal strands of muscle the abdominal tergals, as the 

 ventral sclerites (sterna) of the same region by sheets of 

 abdominal sternals, while vertically directed tergo-stemal 

 muscles connect each tergumwith the sternum of its segment. 

 By the contraction of the last-named muscles the dorsal 

 and ventral walls are drawn together, the capacity of the 

 abdomen being thus reduced and the pressure necessary 

 for respiration exerted on the air-tubes (see pp. 42-3 above). 



