24 SPIDERS [CH. 



experimenter was on the point of drawing interesting 

 conclusions from the behaviour of a spider in response 

 to the notes of a flute, when he found that precisely 

 the same results were obtained by a soundless puff of 

 air. It seems hardly possible to make sure, in the 

 case of a spider in a snare, that the sound vibrations 

 are not felt, apart from any sense of hearing, and it 

 is a remarkable fact that it is only the snare-spinning 

 spiders that make any response to sounds : free- 

 roving spiders are apparently quite deaf. 



In experimenting with sound we must take two 

 precautions: the instrument used must not necessi- 

 tate any marked action which may be visible to the 

 spider, nor must it give rise to palpable air-currents. 

 These requirements are best met by a tuning-fork of 

 not too low a pitch. We cannot feel the air vibra- 

 tions emanating from it, but can only perceive them 

 by the ear, but we have no proof that the spider's 

 sense of touch ceases precisely at the same point as 

 our own. However, no better instrument for experi- 

 ment seems to be available, so we take a tuning-fork, 

 and approach it cautiously in the quiescent state- 

 towards the spider, stationed, we will suppose, in the 

 centre of its snare. No notice is taken, and we care- 

 fully withdraw it, set it vibrating, and approach it 

 again in the same manner. There is now generally 

 a response, the spider raising its front legs and 

 extending them in the direction of the fork, or, if the 



