EMOTIONS. 343 



cially imitate the stimulus which the head of one caterpillar 

 supplied to the tail of the next in the series (and which 

 serves to let the latter known that the series is not inter- 

 rupted), I removed the last member of the series. As always 

 happens when this is done, the next member stopped, then 

 the next, and the next, and so on, till the whole series were at 

 a halt. If I had now replaced the last member with its head 

 touching the tail of the penultimate member, the latter would 

 again have begun to move, then the next, and the next, and 

 so on, till the whole series would again have been in motion. 

 Instead of doing this, however, I took a camel-hair brush and 

 gently brushed the tail of the then last member. Imme- 

 diately this member again began to move, and so set the 

 whole train again upon the march. But in order that the 

 march should continue, it was necessary that I should con- 

 tinue brushing the tail of the last member. Now I found 

 that if I brushed in the least degree too hard, so as not suffi- 

 ciently well to imitate the stimulus supplied by the hairy 

 head of a caterpillar, the animal became alarmed and threw 

 itself upon its side in the form of a coil. I therefore tried 

 the experiment of puzzling the animal, by first brushing its 

 tail gently for a considerable time — so that it should have no 

 reason to doubt, as it were, that I was a caterpillar — and 

 then beginning by degrees to brush it more and more strongly. 

 I could then see that a point came at which the animal was 

 puzzled, so that it hesitated whether to go on or to throw 

 itself upon its side. It appeared to me that at this point the 

 animal began to become alarmed ; for the brushing was still 

 exceedingly gentle, so that if the animal were actuated only 

 by a pure reflex mechanism, I should not have expected so 

 infinitesimally small a difference in the amount of stimula- 

 tion to produce so great a difference in the nature of the 

 response. 



in all particiilars. I am likewise able to confirm all the other points in his^ 

 account of the remarkable habits of these larvae. I may add that as soon as 

 a member of a moving chain is removed, the next member in advance not 

 only stops, but begins to wag its head in a peculiar manner from side to side. 

 This perhaps may serve as a signal to the next member to stop ; bvit, however 

 this may be, as soon as the next one does stop, it also begins to wag its head 

 in the same manner, and so on till all the caterpillars in advance of the 

 interruption are standing still and wagging their heads. And they all 

 continue without interruption thus to wag their heads until the procession 

 again begins to move. I have never seen this pecuhar movement performed 

 except under these circumstances. 



