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Fig. 9 Diagram representing the effect on the behavior of tadpoles of Ama- 

 roucium of sudden changes in the ilkimination of the retina, t, tadpoles swimming 

 along the edge of a drop of water without rotating on the longitudinal axis; I, 

 light rays ; p, paths taken by tadpoles. Note that when the tadpole, in swimming 

 along the edge of the drop, reaches a position in which the longitudinal axis is 

 approximately parallel with the direction of the rays, it suddenly turns sharply 

 and leaves the edge of the drop. In the position to the right this is owing to a 

 decrease and in the position to the left to an increase in the illumination of the 

 retina. 



