THE SENSORY RESPONSES OF CHITON 



213 



cate thermo-receptors, some 'use' would have been found for 

 them. In either event the adaptationist rests intelleetualljr 

 satisfied. It is, nevertheless, a fact, although it may have 

 little 'bearing upon this matter, that the temperature variations 

 endured by Chiton are rather wide. These variations are both 

 diurnal and tidal, and their amplitude, in summer months, ex- 

 tends during the twenty-four hours in some situations from 23°^ 

 to 37°C. ; this is especially the case on hard bare limestone rocks, 

 where the heat of the midday sun at low tide is quite intense. 

 At the time these experiments were made the surface tem- 

 perature of the sea was 26° to 27°C., and this temperature was 

 taken as the 'normal' in the tests that are here described. 



Chitons were immersed in sea-water maintained at the tem- 

 perature noted, and their movements were carefully recorded. 



Behavior of chitons transferred from sea-water at 25° to 26°C. to sea-water at the 

 temperatures indicated at the margin 



TEMPERATDRE 

 IN DEGREES 

 CENTIGRADE 



8° to 10° 



10° 



Ctenidia almost instantly contracted, and remained so for 3 min.; 

 5 min. from time of immersion, all were again expanded. Cte- 

 nidia respond to tactile excitation by contraction, but weakly. 

 No tactile responses obtainable from other regions. No spon- 

 taneous movements; remaining as if anesthetized. 



Ctenidia contracted; began to expand in 2 min. At first, the foot 

 partly curled, as if preparing to roll up, but soon became straight 

 again. Tactile sensitivity soon abolished; after this had been 

 ascertained the foot and mantle were tested with weak HNO3 

 solution, but no reaction resulted. 



Ctenidia contracted within 3.5 min.; after 2 to 4 min. began to 

 expand; fully extended after 4 to 5 min. Ctenidia respond to 

 touch, feebly in some cases. No spontaneous movements of the 

 foot or animal. Responses of the body to touch absent after 15 

 min. 



Foot spontaneously thrown into smooth contractions that lasted 

 2 min. Ctenidia contracted; after 4 min. they relaxed one by 

 one. After 10 min. ctenidia responded to touch. General tac- 

 tile responses very poor. 



Ctenidia contracted after 0.5 to 6.0 min.; expanded after 7 to 10 

 min.; after 10 to 11 min. reactions to touch returned, but very 

 slowly. In several cases after 1 min. immersion the gills began 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 29, NO. 2 



