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S. O. MAST 



Fig. 8 Outline of the anterior' end of tadpole of Amaroucium, showing the 

 effect on the illumination of the retina of slight movements of the source of light. 

 b, body; t, tail; e, section of pigmented eye-cup; a, b, different positions of source 

 of light. Note that if the source of light is to the right of the line a~a the inner 

 surface of the eye-cup which contains the optic nerve-endings is illuminated 

 and that if it is to the left side of this line the inner surface is shaded. Note also 

 that slight movements in either direction from the line a-a may produce profound 

 changes in the illumination on the inner surface of the eye-cup. 



