212 



THE EDITOR'S ALPHABET OF INSECTS, 



abductor muscle, and as it is but very slightly movable, there is no 

 antagonist abductor. 



" The shank has a strong flexor muscle, and a more feeble extensor 

 in each of the three pairs of legs. 



" The foot, in each of the three pairs of legs, has an extensor and a 

 flexor in each of the joints. The last joint includes a flexor and ex- 

 tensor for moving the claws. 



" Standing * of Insects. — The centre of the pressure -j- in insects 

 being usually either in the base of the abdomen or in the hind corselet, 

 the three pairs of legs are of course inserted in advance of it ; and hence, 

 did they stand perpendicular to the body like the legs of quadrupeds, it 

 would be impossible for an insect to alight on its legs without being 

 upset. 



" To obviate this, the legs extend to a considerable length from the 

 body, and not only so, but the first pair project obliquely forward, and 

 the third pair obliquely backward, while the second pair are, in some 

 species nearly at right angles to the body, and in other species, project 

 obliquely forward or obliquely backward, according as the position of 

 the centre of .pressure requires for the stability of the animal. In two- 

 winged flies, for example, the mid pair of legs projects obliquely for- 

 wards, as may be seen in the figure. 



" Figure of a Crane Fly % to show the position of the feet, as extending the base within 

 which falls the line of direction of the centre of pressure. 



" The singular pendulum-like motion, exhibited by some species of 

 long-legged flies while their feet are quite stationary, may be referred 



* In Latin, Statio. + See Alphabet of Physics, p. 38. 



\ In Latin, Tipula oleracea. 



