202 LESLIE B. AREY AND W. J. CROZIER 



sponse to a small volume of n/10 HCl was, however, still ob- 

 tainable. Taken in their entirety, these findings tend to indicate 

 the physiological distinctness of the tactile receptors, although 

 the methods employed in the tests are open to the objection 

 common to all such experiments: we cannot be entirely sure 

 that we are dealing with sources of stimulation which are quan- 

 titatively comparable. Less objection can be taken to the result 

 of experiments of the following kind. If the inner ventral girdle 

 surface, under water, be repeatedly stimulated with small 

 volumes of n/30 HCl in sea-water, four or five successive re- 

 sponses may be obtained from the activation of one area. This 

 area is then exhausted for stimulation in this way. It is, how- 

 ever, still reactive to touch. Since the acid is usually regarded 

 as a more powerful excitant than touch, the objection above 

 referred to may thus be removed. 



2. Vibratory stimuli 



The characteristic statocyst of gastropods is not present among 

 amphineurans. Hence it would be interesting to learn — al- 

 though the theory of the statocyst as a merely positional organ 

 seems now well established (Baunacke, '14) — whether or net 

 Chiton reacts to vibratory stimuli such as sound waves. It 

 proves not to respond to attempted stimulations of this kind. 



Chitons placed in a beaker of thin glass containing sea-water 

 were watched while the lip of the beaker was tapped with a 

 glass rod. No reactions followed this treatment. Sounds 

 transmitted to the beaker from a vibrating saw blade had like- 

 wise no effect. The. table top supporting the beaker was sharply 

 struck, jarred, or rubbed, with the same absence of response. 

 Chitons placed ventral surface upward in shallow water, so 

 that they were just covered, did not react to drops of sea-water 

 falling on them from a distance of 10 to 15 cm. 



A chiton resting upon a glass surface, under water, in some cases 

 responded to a tapping of the glass immediately under the ap- 

 pressed mantle by raising the girdle in that region. If the girdle 

 was already raised, in a few cases only was it lowered to the 



