76 Papers from the Marine Biological Laboratory at Tortugas. 



(6) The reactions of the young turtle are not modified by sound or 

 odor of the sea, nor by a tank of sea-water in which there is not sufficient 

 quantity to give color. 



It might be well to state here that the colors used, both glass and 

 paints, were far from monochromatic, so that their exact values are not 

 known, but at the same time it should be remembered that most or all 

 of the colors in nature are polychromatic. An excess of any particular 

 color seems to give the effect. That we are dealing here with a case 

 of true chromotropism is, perhaps, somewhat doubtful. Indeed, true 

 chromotropism is so rarely met with and so many other factors, as 

 intensity, the "color-blindness" of lower eyes, etc., contribute to it or 

 to startlingly similar reactions, that I have studiously avoided the term. 

 I must also confess myself unable to satisfactorily explain the cause of 

 the response obtained at night on the beach. While the moon shone 

 brightly, the differences in colors were much reduced to the human eye, 

 so much so that, as far as color was concerned, the bushes and the water 

 were practically the same. However, the sea was shiny and the bushes 

 were not. This reaction seems to me to be, as I have before stated, a 

 transitional stage between the color reaction and the photophilous 

 response, but this helps us little in explanation of its ultimate factors. 



In regard to the responses in the daytime, we may speak with a little 

 more certainty, although here, too, the intensity of the colors is a bother- 

 ing element. Practically all the investigators who have worked on color 

 responses have found that blue or the blue end of the spectrum acts as 

 white light and the red end of the spectrum as shadows would in photo- 

 tropic responses. In the case of these loggerhead turtles we find blue 

 chosen in preference to the directive rays of the sun. Whether this 

 indicates a true chromotropism or not we can not be entirely sure. 



The application of the bare facts obtained to their biological signifi- 

 cance in the life of the animal is, I think, clear. Bushes, green in color, 

 grow on all islands of any size, above the high-water mark. The shores 

 of all islands slope down to the water. All turtles' nests are laid just 

 above the high -tide mark, at or near the bush line. The young turtle, 

 hatching out and crawling up to the surface of the sand, avoids the bushes, 

 goes down the shore, and easily finds the water. Once in, the darker 

 blue of the deeper water attracts it out of the dangerous fish-infested 

 shoals of the reefs. 



