170 



S. O. MAST 



of the body as an axis (fig. 7) . Whenever the hght was suddenly 

 reduced by passing the hand down in front of the microscope while 

 the specimen was at rest, it immediately became active, the tail 



Fig. 7 Representing reaction to increase in illumination in Amaroucium 

 pellucidium tadpole loosely held under cover-glass, a, resting position ; b, position 

 assumed after reduction in illumination. Note that the tail is practically straight 

 but that it vibrates as indicated by the arrows. If the illumination is now 

 increased, the tail bends toward the abocular side and the tadpole swings into 

 position c, where the tail again becomes straight and vibrates as indicated by 

 the arrows. If the illumination is now decreased the tadpole returns to position 

 b, or nearly to this position. It usually swings somewhat further after the light 

 is increased than it does after it is decreased. The fact that the tadpole, in 

 response to an increase in illumination, swings from position b, in which the tail 

 is practically straight, to position c, shows that the increase in illumination 

 does not merely inhibit the effect of a preceding decrease, but acts as a stimulus 

 causing the tail to bend toward the abocular side. 



turning toward the ocular side and vibrating rapidly. This 

 caused the posterior end of the body to swing in the opposite 

 direction, (fig. 7, h). Thus it continued to swing usually 90 



