PHOTIC REACTIONS OF TADPOLES 



259 



2. The eye 



From the recorded data and graphic representations it appears 

 that when the eyes and skin of tadpoles are illuminated, the 

 responses are those due to stimuli received through the skin. 

 To test this further, rays of known intensity were concentrated 

 upon the eye only. To avoid stimulation of other parts of the 

 body, the following method was employed. A box measuring 



mv!mm^ 



Fig. 5 Diagram of apparatus for testing the sensitivity of the eye. a,h, a box 

 constructed of heavy black cardboard; k, tightly fitting hollow cone; n, light. 



28 cm. in length and 9 cm. in height and in width was con- 

 structed of heavy black cardboard (fig. 5, a, h) . One end of the 

 box was so modified by a cylindrical projection as to receive 

 a tightly fitting hollow cone {K) terminating in a small opening, 

 shghtly less than the diameter of the eye of the tadpole. A 

 light bulb (n) of '0.3 candlepower was enclosed in the box and 

 the distance from the end of the cone was so adjusted as to give 

 a light intensity of 5 candle-meters at the position of the animal, 

 this being the intensity which proved effective with the experi- 



