SELIG HECHT 



153 



the latent period of nineteen animals gave 1.76 seconds as the aver- 

 age duration of this portion of the reaction time. 



3. The latent period must include the time for transmission of the 

 stimulus and kindred phenomena. There is evidence to show, how- 

 ever, that a great portion of it is concerned with a process occurring 

 in the sense organ itself, as is shown in Experiment 9.4. 



It will be seen that, within limits, the shorter the exposure time 

 (sensitization period) the longer the reaction time, and consequently 

 the latent period. The latent period in the main must therefore take 

 place in a locality where it may be immediately influenced by the 

 amount of light energy received. This would indicate that it is the 

 outward manifestation of the duration of a process within the sense 

 organ itself. 



4, The existence of a latent period of nearly 2 seconds is hardly 

 to be considered as an advantage to the life of the species. The ordi- 

 nary daylight of southern California is deleterious to Ciona. The 

 animals die very soon in an aquarium in diffuse dayhght. When 

 placed near a window they contract and perish in a day, whereas in 

 a dimly lighted room or in the dark they remain in excellent condition 

 for a week or more. They are normally found on the under side of 

 floats. 



The comparatively long delay in responding after a sufficient 

 stimulus has been received cannot thus be of assistance to the ani- 

 mal in its response to a noxious stimulus. It must therefore be 

 attributed to the duration of a chemically necessary process occurring, 

 as suggested, in the sense organ. 



