REACTIONS TO LIGHT IN LARVAE OF ASCIDIANS 



163 



the edge of the enclosure. Others can be loosely held if the cover- 

 glass is carefully pressed down. In some of the tadpoles in 

 which locomotion is thus prevented it is usually found that the 

 tail is rapidly vibrating. If now the light is suddenly reduced, 

 the tail at once bends toward the ocular side and continues to 

 vibrate (fig. 4). In the specimens which are loosely held this 

 bending of the tail results in turning of the body toward the 

 eye, producing a circular course, or if locomotion is prevented it 



Fig. 4 Outline of tadpole of Amaroucium pellucidum representing reaction 

 to decrease in illumination in active specimens, a, position of tail before stimu- 

 lation; b, position of tail after stimulation; arrows, extent of vibration. 



may result in the tail swinging toward the abocular side about the 

 body as a pivot. In either case this movement continues only 

 a very short time, after which the tail may assume its original 

 position or it may bend in the opposite direction, then back again 

 several times before it assumes its original position. 



The time the tail, holds the bent position after reduction of 

 illumination was ascertained in a number of different specimens 

 with a stop-watch. Eight to ten successive readings were 

 made on each individual studied. The averages of the results 



