MOTIONS OF INSECTS. 



359 



a, red spider {Dijsdera cnjthrina). J, the head o( the 

 spider, magnified c o, the mandibles, fringed on the inside with 

 hair, rf, the eight eyes, in form of a horse-shoe. £, the head of 

 the garden spider {Arnnta diadcma). f f f, the eight eyes 



g S, the upper mandililes. A, toothed comb. 



from taking. Perhaps this may help us to account 

 for the singular motions of some of the crane flies 

 (TipnUdcc), while stationary upon a window or a 

 wall, their whole body vibrating alternately outwards 

 and inwards from the wall, with a pendulum-like 

 movement, as rapid, or more so, than the clicking of 

 a watch. Kirby and Spence say, this is produced by 

 the weight of their bodies and the elasticity of their 

 legs; and that, unless it be connected with respira- 

 tion, it is not easy to say what is its object.* To us 

 it appears, like tlie motion of the caged animals just 

 mentioned, to be for the purpose of e.xercising them- 

 selves and of driving the fluids into their long legs, 

 which may not be effected in the exercise of flying on 

 account of their legs then remaining almost motion- 

 less. Others of the same family may be seen hang- 

 ing from a wall or ceiling by their fore-legs, while the 

 hind ones are perked out into the air, and moving up 

 and down in a slow manner, probably to watch against 

 approaching danger, as they are very timid; and if 

 the door of the room where they are be hastily opened 

 or shut, or if any other agitation of the air be pro- 



Intr. ii, 306. 



