HEARING IN INSECTS. 75 



just before their moulting than at any other time.* 

 This also, as it happens, was the very period when 

 Bonnet made his observation, as he expressly says, 

 ' some of them had undergone, and others were 

 about to undergo their first moult. ' 



Bonnet imagined, however, tliat he had proved his 

 opinion by a similar experiment upon caterpillars of 

 another species, which also live in society a part of 

 their lives. ' VVhile they were exposed, ' he says, 

 * to a burning sun, and ran quickly from one side to 

 another, I bethought myself of ringing a small bell 

 at a very short distance from the nest : some of them 

 stopt instantly and briskly agitated the fore- part of 

 their bodies, as if they felt the sound of the bell dis- 

 agreeable.' f It is unfortunate that, from Bonnet's 

 inattention to system, we cannot tell the species of 

 the caterpillars on which the experiment was tried ; 

 but we have repeated it in a number of cases, both 

 with social and solitary caterpillars, without being 

 able to verify his observations. At the time of wri- 

 ting this, we tried the effect of a great variety of 

 sounds upon a nest of the brown-tail moth [Porthesia 

 aurifliia) — most probably Bonnet's species — soon 

 after their first moult, but we were unable either in 

 the sun or the shade to produce any effect upon them 

 by sounds ; and several full-grown caterpillars of 

 the fox-moth {LasiGcampa Rubi, Schrank) in a box 

 beside them appeared equally insensible. 



We are thus inclined to explain Bonnet's second 

 experiment as we did the first, though his own ac- 

 count is not improbable ; for all caterpillars are rather 

 sensitive, and jerk themselves when touched, particu- 

 larly should any of their companions come upon them. 

 In most cases the jerk succeeds in driving away 

 the intruder ; but in the cannibal species it only serves 

 as a cause of irritation which leads them to plunge 



* J. R. + CEuvres, ii, 37. 



