272 MOTIONS OF INSECTS. 



and safety, by the help of their webs, or some other 

 artiSce, to make their bodies lighter than the air^." 



Since the motions, and instruments of motion, of in- 

 sects are usually very different in their preparatory 

 states, from what they are in the imago or perfect state, 

 I shall therefore consider them separately, and divide 

 my subject into — motions of larvae, — motions of pups, 

 — and motions of perfect insects. 



I. Amongst hirvce there are two classes of movers — 

 Apodous larvae, or those that move without legs, — and 

 Pedate larvae, or those that move by means of legs. I 

 must here observe, that by the term legs^ which 1 use 

 strictly, I mean only jointed organs, that have free mo- 

 tion, and can walk or step alternately ; not tliose spu- 

 rious legs without joints, that have no free motion, and 

 cannot walk or take alternate steps ; such as support 

 the middle and anus of the larvae of most Lepldoptcra 

 and saw-flies (Ttnthredinidce). 



Apodous larvffi seldom have occasion to take long 

 journeys ; and many of them, except when about to as- 

 sume the pupa, only want to change their place or pos- 

 ture, and to follow their food in the substance, whether 

 animal or vegetable, to which, when included in the 

 egg, the parent insect committed them. Legs there- 

 fore would be of no great use to them, and to these 

 last a considerable impediment. They are capable of 

 three kinds of motion ; — they either walk, or jump, or 

 swim. 1 use walking in an improper sense, for want of 

 a better term equally comprehensive : for some maybe 

 said to move by gliding ; and others by stepping (I mean 



° PliysicG-Thcol. Ed. 13. 363. 



