THE SENSORY RESPONSES OF CHITON 203 



glass surface as a result of the tapping. In several instances 

 chitons treated in this way began to creep, and in one case began 

 to creep backward. 



There is no suggestion of the perception of vibratory stimuli in 

 these results. Direct contact excitation is quite effective, but 

 vibratory disturbances, such as sound waves, seem not to be 

 reacted to. In collecting chitons it is advantageous to employ 

 a large cold-chisel and a hammer; yet one finds that the removal 

 of several members of a group, involving repeated and fairly 

 heavy blows, does not usually result in near-by chitons becoming 

 firmly attached to the rock, unless they have been directly 

 affected by a deforming pressure. This deficiency cannot be 

 attributed to the absence of a statocyst, however, since other 

 moUusks, well provided with statocysts, are known not to react 

 to vibratory disturbances. 



A chiton may be suspended in water by having the beak of one 

 shell plate clamped in forceps attached to a support. Under 

 these circumstances it does not react to vibratory disturbances 

 transmitted through the water. 



3. Thigmotaxis 



The surface of the foot of Chiton, if touched locally, draws 

 away in a rather sharp pucker, especially if a sharp point be 

 used. No attempt is made to attach the stimulated spot by 

 suction, and if the activation is repeated the resulting movements 

 of the foot are such as to cause its removal from the region of 

 stimulation. If, on the other hand, a larger surface, such as the 

 flat end of a pencil, be applied, the foot becomes firmly affixed 

 to the foreign surface, and is pulled deeply down below the gen- 

 eral level of the rest of the foot. The minimal area reacted to by 

 attachment is about 5x5 mm. for chitons 6 to 9 cm long, as 

 Parker found ('14). 



It is important to note that w^hen a pedal wave has formed 

 and is traveling down the foot of a chiton lying on its back, the 

 surface of the foot immediately involved in the wave can attach 

 to a small point (e.g., the pointed end of a pencil) very firmly 

 by suction. 



