220 LESLIE B. AREY AND W. J, CROZIER 



annulled. Immersion in water at 15° frequently led to a few- 

 contraction waves appearing on the foot and to movements of 

 the palp, although the ctenidia did not move. Below 8° these 

 movements of the foot were not seen. Between 20° and 38° these 

 movements were absent. The response of the ctenidia to low 

 temperatures is particularly definite and resembles the contrac- 

 tion of the oral tentacles of holothurians (Crozier,'15 b; Olmstead, 

 '17 b), appearing at about the same temperature. These re- 

 sponses are more clearly indicative of thermal receptivity in the 

 strict sense than are those to high temperatures, for below 15° 

 the tactile sensitivity of Chiton quickly diminishes, whereas at 

 38° to 40° the tactile irritability of the ctenidia, foot, and palp, 

 leading to responses identical with those obtained in the heat 

 treatments, is greatly enhanced for several minutes subsequent 

 to immersion; the augmentation in responsiveness to touch is 

 greater at 40° than at 38°, but at both temperatures sensitivity 

 to touch decreases to below normal after ten minutes and at 

 higher temperatures it disappears more quickly still. 



So far, then, we believe that in Chiton there is evidence of 

 something akin to cold reception, but that there is reason to 

 regard the responses obtained upon immersing the animals in 

 warmed sea-water as the result of increased tactile irritability or 

 of some related, non-thermospecific type of irritability. 



2. Local application of heat and cold 



There is reason to believe that the responses of many animals 

 to chemical influence, for example, and possibly to heat, differ 

 considerably when, 1) a small area of the integument is affected 

 by the stimulation, and, 2) the whole surface is simultaneously 

 exposed to activation. For this reason, and also with the purpose 

 of locating the regions mainly concerned in thermal receptivity 

 (if any should be found), it was necessary to carry out tests in 

 which small portions of the surface of Chiton could be locally 

 heated or cooled. These tests were made in several ways, by the 

 application of small volumes of sea-water at different tempera- 

 tures or by the use of heated or cooled solid objects. Chiton is 



