328 G. H. PARKER 



In a final set of experiments designed to test the effects of the 

 overhead and the horizontal fields of light, I had an excellent 

 opportunity to observe the exact method of response of the turtles 

 to their illuminated surroundings. Two large collecting tubs 

 were placed upon a sea-wall, one right side up and the other bot- 

 tom up. The tubs had a diameter of about 50 cm. and a height 

 of a Uttle over 30 cm. Five turtles were tested by being placed 

 alternately on top of the inverted tub at its center and inside the 

 upright tub likewise at its center. From the top of the inverted 

 tub the turtle could see the whole landscape; from inside the 

 upright tub it could see only the overhead sky. From both 

 positions the turtles were free to move in any horizontal direction. 

 In each set of tests a given turtle was headed successively north, 

 east, south, and west. The sea-wall on which the tubs were set 

 ran approximately north and south; to the west was open water; 

 to the east a field with trees and shrubbery. In the twenty tests 

 inside the tub the turtles remained stationary for five minutes in 

 fourteen instances and in the remaining six they took various 

 courses which may be roughly described as twice to the northwest, 

 twice to the east, once to the northeast, and once to the south- 

 west, showing that the overhead sky had no effect on their 

 orientation. In the twenty tests on the outside of the tub the 

 turtles went invariably to the west, awaj' from a horizon inter- 

 rupted by trees and shrubbery and toward one of open water. 

 But the interesting part of these tests was not so much the direc- 

 tion taken b}^ the turtles as the way in which this direction was 

 apparently discovered. WTien the j^oung turtle was 'set at the 

 middle of the inverted tub, it rested there quieth' about half a 

 minute, raised its head high in air, made a complete circle or more 

 in a very restricted area, and then moved off immediately to the 

 west. The preliminary circular movement, almost always a 

 complete circle or more, was made irrespective of the position in 

 which the turtle was set. To all appearances it seemed as though 

 the animal tested first the whole horizon and then moved in a 

 direction away from large masses and toward greatest openness. 



In describing the photic responses of the young loggerhead, 

 Hooker uses the terms photophilism and phototropism ('11, p. 71) 



