384 INSECT TRANSFORMATIONS. 



little bird lives on water insects and the fry of fish, 

 its amphibious powers are indispensable. 



Some of these aquatic insects, such as the whirlwig, 

 are so highly polished, that the water will not adhere 

 to their bodies; while others (Hydrophili, &c,) are 

 covered below with a thick coating of silky hair, which 

 repels the water and usually surrounds them with a 

 globule of air that shines under water like quicksilver. 

 The spider mentioned above is similarly furnished with 

 downy hair for the same purpose. 



In walking, insects exhibit endless peculiarities. 

 The hunting spiders, and many of the midges (Psy- 

 chodce, LATR.), instead of walking straightforwards, 

 most usually walk obliquely, and often at right-angles 

 to the line of their own bodies; while most insects 

 can, when it is necessary, walk directly backwards 

 with almost as much facility as forwards. When 

 the centipedes (Scolopendridce, LEACH) walk back- 

 wards, they only use their four hind-legs, and these, 

 when they walk in the usual way, are not employed, 

 but dragged after them like the locked wheel of a mail- 

 coach in driving down a steep hill. It was first 

 observed, we believe, by Kirby, that a millepede 

 common under stones, the bark of trees, and the 

 hollow stems of decaying plants, and pro vinci ally 

 called maggy-manyfeet (Jttt*a terrcshis), performs 

 its serpent-like motion by extending alternate por- 

 tions of its numerous legs beyond the line of the 

 body, while those in the intervals preserve a vertical 

 direction. So long, then, as it keeps moving, little 

 bunches of the legs are alternately in and out from 

 one end to the other of its long body, the undulating 

 line of motion successively beginning at the head and 

 passing off at the tail.* We may add, that the form 

 and structure of this insect are admirably adapted 



* Intr., vol. ii, p. 309. 



