330 G. H. PARKER 



sequently I am not in a position to add anything to this aspect 

 of the subject. I am nevertheless convinced that beside color 

 the photic complexity and photic simplicity of the region of the 

 horizon, as has already been detailed, are factors of first impor- 

 tance in determining the direction of locomotion, for in a number 

 of my tests, as for instance those in the open field, natural blues 

 even in the sky were often absent. Hence I conclude that, quite 

 aside from the effect of color, the direction of locomotion of young 

 loggerhead turtles is significantly influenced by the interrupted- 

 ness or openness of the region of the horizon. 



On beaches locomotion down a slope, away from an interrupted 

 horizon and toward an open one, as well as toward masses of blue, 

 M'ould almost invariably lead to the sea. These doubtless are the 

 chief factors that influence the course of the newly hatched 

 loggerhead turtle whereby it reaches the ocean. Although water 

 is the environment to be attained, water in itself plays no part in 

 directing the movements of this animal which are indirectly 

 influenced by those features of the environment just enumerated. 

 It would be interesting to ascertain whether any of these factors 

 affect Fundulus in its escape over the beach to the sea from small 

 pools as described by Mast ('15). 



CONCLUSIONS 



Newly hatched loggerhead turtles find their way from their 

 nests to the sea in consequence of at least three factors: first, 

 their positive geotropism as shown in their tendencies to move 

 down slopes (Hooker); second, their response to their retinal 

 images in that they move toward regions in which the horizon 

 is open and clear, and away from those in which it is interrupted, 

 and, third, their probable response to color in that thej^ move 

 toward blue areas rather than toward those of other colors 

 (Hooker) . 



These animals are not appropriately described as either nega- 

 tively or positively phototropic, but are to be regarded as exhibit- 

 ing a more complex condition, in that they respond to the details 

 of their retinal images rather than to these images as wholes. 



