

iv] MENTAL POWERS OF SPIDERS 25 



sound is loud, dropping suddenly by a thread and 

 remaining suspended some inches below the snare. 

 The experiment should be repeated several times 

 with the fork sometimes still, sometimes vibrating, 

 and the conclusion arrived at will be that the spider 

 is aware of the vibrating fork but by which sense ? 

 It is noteworthy that a fork giving a low note is 

 alwavs most effective. 



V 



Now here is a very remarkable fact. In two 

 widely different groups of spiders the Theraphosidae 

 or so called " bird-eating spiders" and the Theridiidae 

 -there are species with a stridulating or sound- 

 making apparatus, and we should hardly expect a deaf 

 creature to evolve an elaborate mechanism for the 

 production of sound. This is a matter, however, that 

 we shall discuss later. 



No amount of research has succeeded in localising 

 the sense of hearing in spiders, supposing it to exist. 

 The creature may lose any of its five pairs of limbs 

 (four pairs of legs and one pair of pedipalps) without 

 alteration in its response to sound. If the front legs 

 are missing the second pair are raised when the vibrat- 

 ing fork is approached. 



It is fairly easy to test the sense of smell in these 

 creatures, the only necessary precaution being that 

 no acid or pungent substances capable of having an 

 irritating effect on the skin, such as vinegar or 

 ammonia, must be employed. Such perfumes as 



