350 THE BIOLOGY OF THE FROG chap. 



they go toward the green ; in general it may be said that 

 where they are able to go toward one of two colors of equal 

 intensity they move to the color lying nearest the violet end 

 of the spectrum. 



The eyes would naturally be regarded as the organs 

 through which the phototactic response is effected, and in 

 fact they play an important part in the process, but, as 

 Dr. Parker has recently shown, orientation may be brought 

 about merely by the photic stimulation of the skin. In 

 order to determine the role played by the eyes in phototaxis 

 Dr. Parker covered a frog with the skin of a somewhat 

 larger individual leaving only the eyes, feet, and snout ex- 

 posed. Four specimens thus covered were tested, and it 

 was found that they " turned toward the light and jumped 

 toward it much as normal frogs do." When a normal frog 

 was introduced for comparison, it was found that in most in- 

 stances it " responded more quickly than the covered one, 

 but the difference was not so great that it might not have 

 been due to the purely mechanical interference of the cover- 

 ing skin." When the eyes of the frog were covered as well 

 as the skin, there was no. longer any response to light, thus 

 showing that it was not the light, which may have pene- 

 trated the covering of dead skin, that effected the orienta- 

 tion. 



That phototaxis may be produced through the skin alone 

 as well as through the eyes alone was shown by Parker in 

 the following experiment. Eleven frogs were taken, and 

 " by a single vertical, transverse cut just behind the eyes, 

 these organs and the cerebral hemispheres were removed 

 with the snout of the animal. It is well known that frogs in 

 this condition may with a little care be kept alive for many 

 weeks, and that the chief difference between these and 

 normal frogs is the great reduction in spontaneous move- 



