Sensory Discrimination: Hearing 119 



sound. When both statocysts were removed, the reactions 

 were still made, but not so markedly nor at so great a dis- 

 tance from the sound. A similar response to the striking 

 of a partially submerged glass jar was seen in a decapod, 

 Virbius zostericola, which has no statoliths (616). Mysis 

 has been found to react to sounds when the statocysts are 

 destroyed (48). 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 pro- 

 duced in the earth, for instance by stamping (616). No 

 sound reactions have been found in the crayfish (40). In 

 short, such responses to vibrations as occur among the 

 Crustacea seem affairs rather of mechanical than of true 

 auditory stimulation ; nevertheless Be the (48) and Hensen 

 (295) are both inclined to believe, as did Delage, who first 

 called attention to the static function of the statocysts 

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

 sense" of Crustacea will be discussed later. 



33. 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 (166, 167), 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 (616). 

 When various species of spiders were tested by holding 



