STRANGE MODES OF PROGRESS. 193 



quenters of our windows in early spring, and again towards 

 autumn, usually move in an oblique direction ; and in the 

 celebrated grub of the ant-lion we are furnished with an 

 instance of a tardy mover with whom to walk backwards is the 

 only mode of travelling. 



Who would expect to find anywhere, save in the thinly- 

 peopled world of monsters, a creature with legs upon its back? 

 Yet have two such been discovered in the world of insects : 

 one, the bat-louse,* which is described as being able to trans- 

 port itself with marvellous celerity from one end to the other 

 of the furry forest wherein it dwells ; the other, the grub of 

 a little gall-fly,t which inhabits one of the berry-shaped galls 

 common upon oak-leaves. The latter can have, of course, but 

 little room for exercise; but Reaumur, its discoverer, can 

 hardly be mistaken in supposing that the singular position of 

 its legs, in the centre of the back, is that of all others best 

 adapted to its hollow sphere of action. 



Some insects, again, are not only remarkable for the number 

 of their legs, but also for the remarkable way in which they 

 use them. 



" When centipedes walk backwards, 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 coach in driving down a hill. It was first observed, we 

 believe, by Kirby, that a millipede, common under stones, the 



* Nycteribia Hermanni. t Cynips Quercus inferno. 



