216 LESLIE B. AREY AND W. J. CROZIER 



normal life conditions of the several animals involved is by no 

 means precise. The temperature producing rapid death in 

 Chiton is a little higher than that found for many shallow-water 

 species in tropical seas (Mayer, '14), but the maximal temperature 

 successfully withstood for a short time (40°) is not noticeably 

 greater than that for other animals which do not live upon sun- 

 baked rocks. Shelf ord ('16) has insisted upon the correlation 

 between the survival time of organisms (of the same and of 

 different species) at elevated temperatures and the character, 

 and especially the depth below the surface, of the habitats which 

 they severally frequent. Doubtless these correlations result, at 

 least in part, from the gradual effects of temperature upon the 

 composition of the body, since they can be determined experi- 

 mentally (Loeb and Wasteneys, '12); although in just what way 

 they operate, we do not know. 



We are chiefly concerned, however, with evidence bearing 

 upon the possibility of a thermal sense, or senses, in Chiton. The 

 'spontaneous' behavior of the gills is perhaps the most significant 

 evidence upon this point, although the nature and variation of 

 the tactile responses are also illuminating. When immersed 

 in sea-water at temperatures of 15°C. or below (down to 8°) the 

 foot of Chiton produces a few smooth contractive movements, 

 which are usually not produced at temperatures between 15"" 

 and 38°. The labial palp also moved slightly. The intensity of 

 these movements increased as lower and lower temperatures 

 were employed, down to about 8°. The ctenidia contracted in 

 sea-water at 10°, and subsequently expanded; there is no regular 

 increase in the vigor or duration of this response with lower tem- 

 peratures, but it continues clearly down to 2°. The abolition of 

 all responses, more quickly the lower the temperature, possibly 

 interferes with the production of other, slower movements which 

 might otherwise result from sensory activation at the lowest 

 temperatures used. With elevated temperatures, not until 40° 

 is reached do we find even slight indications of movements, of 

 both foot and ctenidia, resulting from immersion. Above 43° 

 these movements did not appear in any form. 



