THE SENSORY RESPONSES OF CHITON 193 



In the more critical experiments we made use of a method of 

 graphic registration, subsequently described. 



A. Dorsal surface, a. The shell plates appear not to be sensi- 

 tive to touch. No responses were obtained when the surface 

 of the tegmenta was hghtly touched. (This is further considered 

 on a subsequent page.) 



h. The mantle between the tegmenta, i. e., the tissue covering the 

 insertion plates, may be somewhat exposed, when Chiton is at- 

 tached and 'at rest,' by the separation of the shell plates through 

 the extension of the body. When the mantle was touched in this 

 region the plates immediately adjacent to the site of stimulation 

 were quickly approximated, covering the mantle area which had 

 been touched. 



c. The girdle. When Chiton is attached, the lateral extension 

 of the mantle, known as the 'girdle,' which is flexible, is locally 

 lifted from the substrate unless the animal be disturbed. Under 

 water the girdle may be completely removed from contact with 

 the rock or other surface, but in air this elevation is usually 

 local and commonly takes the form of slight puckerings of, at 

 most, a centimeter or so in length. .To a single touch the girdle, 

 where elevated, responds by local lowering to the substrate at 

 the point of excitation. A more vigorous touch causes a greater 

 extent of the elevated girdle to be lowered. Four or five moder- 

 ate touches in succession affect a still greater length of the 

 girdle, as much as one-quarter to one-third of the circumference, 

 and the time elapsing before recovery to the original elevation is 

 longer than that following a single touch. Even when the 

 girdle has not perceptibly removed from contact with the sub- 

 stratum, it responds by a detectable 'tightening,' or flattening. 

 Several successive touches upon a ' flattened' region of the girdle 

 induce near-by elevated parts to return to the substratum.' Un- 

 less the excitation is continued for nearly one minute, however, 

 or is in the first place very vigorous, the response to touch is 

 strictly homolateral. The anterior end of the girdle is more 

 reactive than the middle or posterior parts, and its peripheral 

 border is more sensitive than the rest of its dorsal surface. 



A chiton quietly creeping in water, with the girdle lifted, re- 



