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, that he had proved his 

 opinion by a similar experiment upon caterpillars of 

 another species, which also live in society a part of 

 their lives. " While 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 t." 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 

 auriflua) 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 (Lasiocampa 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. t CEuvres, ii. 37. 



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