THE SENSORY RESPONSES OF CHITON 



215 



TEMPERATURE 

 IN DEGREES 

 CENTIGRADE 



44° 



45' 



No reactions to touch obtainable after 2.5 to 4 min., from either 

 foot, palp, or ctenidia. 



After 15 min., the foot and mantle are much bloated. 



No movements of the foot; no responses to stimulation. Chiton 

 attached to a glass plate raised the mantle, except at either end, 

 but remained passively attached, after death, for 10 min. Died 

 in 2 min. 



Chitons straightened out and the shell and foot became convex. 

 No responses. Died at once. Animals attached to a glass plate 

 showed slight writhings of the foot when first immersed, due 

 probably to slow warming up through the glass. 



These tests show that sudden changes in temperature between 

 15° and 40°C. have Httle in the way of direct sensory effect upon 

 Chiton when the whole animal, having previously been maintained 

 at about 27°, is suddenly immersed in sea-water of any temperature 

 between these limits. Below 15° an 'anaesthetized' condition is 

 quickly arrived at (Matisse, '10); above 40°, sensitivity quickly 

 decreases. Temperatures of 44° to 45° are almost instantly 

 fatal, although Chiton will survive for nearly two hours after 

 sudden transference to a temperature of 40°. This is the highest 

 temperature which they will successfully withstand for more than 

 fifteen to twenty minutes, and is but a few degrees above the 

 summer temperature sometimes experienced for a similar period 

 in their natural habitat. The factor of safety is here, conse- 

 quently, very small, as compared even with that of other littoral 

 animals of the tropics, which as a group live in the upper zone of 

 temperatures compatible with life (Mayer, '14). The smallness 

 of this safety factor, and the actual magnitude of the temperature 

 quickly producing death, as compared with that for other forms 

 frequenting near-by localities, is sufficient to show that there is 

 little or no trace of adaptational modifications correlated with 

 external thermal conditions. Thus, among animals which have 

 been studied at Bermuda we find such facts as those set forth in 

 table 2, where it will be seen that although there is an undoubted 

 general correspondence in the upper temperature limits, or 

 thermal death points, the correlation of these values with the 



