PHOTOKINETIC REACTIONS OF FROG TADPOLES 



365 



mal (A) was decidedly black due to the expansion of the pigment 

 cells, some of which had even invaded the cornea. This was also 

 noticed in other Amphibian larvae by Laurens ('15), who re- 

 ported that ''after a blind of black shellac or celloidin was 

 placed over the eye for long periods, the cornea was found thick- 

 ened and invaded by pigment cells." It was again observed 

 that the skin of the tail was the most sensitive, for when a 

 beam of Hght was directed upon it the response was more vigor- 

 ous than when directed against the body. The record of an 

 animal adapted to darkness for seven days is shown in table 2, 

 the per cent of photokinesis being 17.2. 



TABLE 2 



Animalb* adapted to light were tried at different periods of 

 adaptation, and the per cent of photokinesis and type of move- 

 ments were substantially the same as those obtained with nor- 

 mal animals. It was observed that the per cent of photoki- 

 nesis did not decrease with the length of the period of adaptation 

 as much as would be expected. The record of an animal adapted 

 to hght for 148 hours is given in table 3. The per cent of pho- 



TABLE 3 



LIGHT ANIMAL (J 



Amount activity 



Number of seconds 

 Per cent 



Number of movements. 



.\ver:ige in seconds 



A.MOUNT OF ILLU.MINATION 



500 c. 1). 



508 

 57 

 20 

 15.4 



100 c. p. 

 Sp3nc3r 



448 

 50 



20.5 



16 c. p. 

 Spencer 



332 

 37 

 35 

 10.6 



'Darkness' 



244 

 27 

 29 

 12.4 



