74 Papers from the Marine Biological Laboratory at Tortugas. 



turtles could see the ocean and the surf through the glass, but it was, 

 of course, a colored ocean when thus viewed. The other conditions were 

 the same as for series A in the experiment with the transplanted bushes. 

 Three glasses were used, differing in color, green, orange-red, and blue. 

 They were tried in the order named. Five turtles were tried in each 

 experiment, each one giving four trials, facing in turn north, west, east, 

 and south. Although they could see a green ocean perfectly well when 

 the green glass was used, their avoiding reaction to green took them up 

 the bank and away from the water in every instance. When the orange- 

 red glass was used, there was a similar avoiding response, but when the 

 blue glass was used, all the individuals in all their trials were strongly 

 attracted to it. I had no red glass, so a red sheet of cardboard was used 

 instead. To this they all responded with the avoiding reaction. 



A series of experiments was made in Pit B by setting up blue glass 

 or blue cardboard on one side and another colored glass or cardboard 

 (red, green, or orange) opposite, and placing the turtles between the two. 

 In every case they went to the blue. Controls with blue alone showed 

 the same result, while a negative response was always obtained when 

 blue was absent and one of the other colors present. 



A series of experiments was tried at night with 9 turtles on the 

 northern end of the key just beyond Pit B. It was a bright, moonlight 

 night and the bushes and other objects on the point, as well as the sea 

 on the east and west, were plainly visible. The turtles were placed one 

 at a time at about 6 feet north of Pit B. The operator retired as far as 

 possible, still keeping the subject in sight, and the turtle was allowed to 

 go at will. All the turtles turned north at first until they reached a 

 point on the central ridge of the sandspit from which the ocean was 

 visible in either direction. Then the course was changed toward the 

 west in 5 cases and toward the east in 4. The route to the water was 

 not a direct one, but was either northwest or northeast, the point of 

 entering the water varying from 75 feet (in one case) to 250 feet from 

 the starting-point. The position of the operator was again an entirely 

 negligible quantity. This series of experiments is of particular interest, 

 as it seems to be 'a combination of or a transition reaction between the 

 response to colors and the purely photophilous response which they 

 do give. 



All of these experiments recorded above were performed in the 

 open air, under surroundings as nearly natural as possible. In addition 

 to these, certain experiments were performed under a rigidly restricted 

 environment to test their phototropic response. 



Dr. L. J. Cole, 1 of the University of Wisconsin, found that "animals 

 having image-forming eyes and which are positively phototropic, respond 

 to a large area of light of comparatively low intensity rather than to 

 an illuminated point of high intensity." The apparatus which he used 

 was highly complex and entirely beyond the facilities at my disposal. 

 Nevertheless, I made a much cruder and simpler form on essentially 

 the same plan and tested several young loggerheads. While they are 



1 Cole, Leon Jacob, An Experimental Study of the Image-forming Powers of 

 Various Types of Eyes. Proc. Am. Acad. Arts and Sci., vol. XLII, No. 16, 1907. 



