THE SENSORY RESPONSES OF CHITON 221 



.easily employed for such experiments because it can be tested in 

 air, the disturbing influence of a sea-water medium being thus 

 eliminated. 



These tests resulted, however, merely in the confirmation of those 

 made by immersing the chitons in sea-water at different temper- 

 atures. Even a red-hot needle directly applied to the surface 

 elicited at most but a slight and very local reaction, on the foot 

 and head ; the mantle beneath the girdle, the dorsal surface of the 

 girdle, the tegmenta, and the mantle between the plates were 

 quite insensitive. The reactions of the foot and palp, although 

 slight, followed the application quite promptly (within 0.4 sec- 

 onds). No responses from any region were obtained when a red- 

 hot glass rod was brought within 2 mm. of the animal's surface. 

 A cooled glass rod (at about 5°C.) induced no responses other than 

 those attributable to tactile irritation. With care, a glass rod 

 could be applied even to the gills without leading to a reaction; 

 this was also true with a cooled rod. 



Similar results were obtained by the use of test-tubes contain- 

 ing water at different temperatures. 



Sea-water adjusted to different temperatures was gently poured 

 in 0.5 cc. volumes from a pipette over different regions of Chiton 

 (in air). At 40°C., local movements of the palp and foot were 

 induced, and a rather indefinite contraction of those ctenidia 

 directly affected; when water at this temperature, or even at 37°, 

 was applied to the dorsal mantle between the plates of an extended 

 chiton, the two neighboring plates were approximated, just as 

 with tactile irritation of this region. Water at 12° led to slight 

 movements of the foot and palp; at 9° to 10°, to prompt local 

 contractions of the ctenidia. Between 12° and 40° no activation 

 was obtained from the general surface. 



Although these results are throughout consistent with those 

 outlined in the preceding section, their interpretation presents 

 some difficulties. An attempt was therefore made to separate, 

 through differential exhaustion, the processes of thermal re- 

 ception from those for tactile and chemical stimulation. The 

 responses to heat and cold indicated that the reactivity of the 



