364 



WILLIAM H. COLE AND CARLETON F. DEAN 



Whether hght or 'darkness' was used first in the trials seemed 

 to make no difference in the per cent of photokinesis. 



The skin was observed to be very sensitive, especially the 

 tail region, for a beam of strong light du-ected against the tail 

 caused a more vigorous response than one directed against the 

 body. It was also observed man}^ times that when a small beam 

 of high intensity was directed on the tail the animal v,^ould do 

 one of two things: remove its tail from the light, or swim \dgor-. 

 ously about the jar for several minutes. 



The results of seventeen trials ^^ith fifteen normal animals 

 showed decidedly photokinetic reactions. In four of these 

 trials positively phototropic reactions were also evident, the 

 results of them being discussed under 'Phototropism.' A record 

 of a typical trial with a normal animal is given in table 1, 

 showing a photokinesis of 23 per cent. 



TABLE 1 



Amount activity 



Number of seconds 

 Per cent 



Number of movements. 



Average in seconds 



AMOUNT OF ILLUMINA- 

 TION 



100 C. p. 



Spencer 



450 

 oO 

 2.3 

 19.5 



'Darkness 



242 

 27 

 44 

 5.5 



Contrary to our expectations, the per cent of photokinesis of 

 dark adapted animals was found to be about the same as that of 

 the normal animals. The type of movements was also similar, 

 except that the difference between the movements in 'darkness' 

 and those in light was much more marked than in normal 

 animals. 



The melanophores of the dark adapted animals observed 

 with the binoculars were found to be fully expanded, a condi- 

 tion existing after short periods of adaptation, as well as after 

 longer periods. There was no discernible increase in the per 

 cent of photokinesis with the increase in the amount of adapta- 

 tion, even for the longest period of thirty-two days. This ani- 



