164 



PHOTIC SENSITIVITY OF CIONA INTESTINALIS 



that the "dark" reaction of sensitive material regeneration is com- 

 paratively slow; second, that the "light" reaction changes the sensi- 

 tive material into its precursor according to the Bunsen-Roscoe law; 

 and third, that in order to act as a stimulus, the light must form 

 such a quantity of precursor that it will bear a definite ratio to the 

 amount of precursor already present. 



2. There is a phase of these data on regularly repeated stimulation 

 to which attention has already been called (Hecht, 1918, c) and which 

 must be emphasized. The individual experiments were ended when 

 the animal failed to react to the light. The course of an experiment 



T.6 



I.Z 



Logar/fhm of Sensiffzation-Penod 



Fig. 5. Data of three other individuals plotted similarly to lower curve of 

 Fig. 4. 



was therefore as follows. The reaction time to the same intensity 

 became larger and larger and finally the animal ceased to react,— 

 because "adapted" to the stimulus. This is the kind of evidence 

 which has been used to prove the existence of a "higher behavior" in 

 lower animals (Kinoshita, 1910). According to this Kne of reasoning, 

 the increased reaction time represents a process of learning, and the 

 complete cessation at the end a condition of "indifference" to the 

 stimulus, or a state of adaptation. 



I hope that the experiments presented in this communication will 

 show the futihty of such merely verbal explanation. From the data 



