Sensory Discrimination : Hearing 109 



sound. A similar response to the striking of a partially 

 submerged glass jar was seen in a decapod, Virbius zos ten- 

 cola, which has no statoliths (349). Mysis has been found 

 to react to sounds when the statocysts are destroyed (27). 

 The fiddler crab, which is amphibious, responds in water to 

 vibrations by retreating slowly from the vibrating walls, and 

 does the same when blinded and deprived of its statocysts, 

 but gives no reaction when the antennae and antennules are 

 removed. On land these animals do not respond to sounds, 

 only to vibrations produced in the earth, for instance by 

 stamping (349). No sound reactions have been found in 

 the crayfish (21). In short, such responses to vibrations as 

 occur among the Crustacea seem affairs rather of mechanical 

 than of true auditory stimulation; nevertheless Bethe (27) 

 and Hensen (164) are both inclined to believe, as did Delage, 

 who first called attention to the static function of the statocysts 

 (97), that they may be auditory organs also. The "static 

 sense" of Crustacea will be discussed later. 



35. Hearing in Spiders 



In spiders the same difficulty arises, of deciding whether 

 the reactions to sound are tactile or auditory. There are no 

 statocysts, but the delicate hairs on the body and legs of the 

 animal have been held to be auditory organs. Dahl, a 

 number of years ago, found them responding to the tones of a 

 violin (86, 87), but this test, which Hensen applied to Mysis, 

 is of very doubtful significance ; as Prentiss suggests, the hairs 

 on the back of the human hand do the same (349). When 

 various species of spiders were tested by holding tuning forks 

 near them or their webs, only the web-making species gave any 

 response. These latter would not react to ordinary noises, 

 nor to the sound of a small fork, but to the humming of a 

 large fork they responded always by raising the front legs, 



