156 



S. O. MAST 



in front of a window in the dark-room. This window could be 

 rapidly closed and opened by means of an opaque shutter 

 carried on a horizontal track. The specimen w^as allowed to 

 come to rest with the window entirely open. By observing the 

 effect of rapidly closing the shutter to various extents, the 

 minimum reduction in illumination necessary to produce a re- 



TABLE 1 



Indicating the time in hundredth-minutes that Amaroucium tadpoles remain active 

 after having been stimulated by sudden reduction in illumination 



sponse was approximately ascertained and the magnitude of the 

 response under minimum stimulation noted. Then, beginning 

 each time with the shutter entirely open, the illumination was 

 variously reduced, but always much beyond the minimum nec- 

 essary to produce a response. Under each of these reductions 

 the magnitude of the response was ascertained. This could be 

 fairly accurately done by noting the relation between the tip of 



