72 Papers from the Marine Biological Laboratory at Tortugas. 



they were distinctly photophilous when swimming in the aquarium, I 

 very carelessly neglected the overhanging bushes on the eastern side of 

 the pit and seized upon their apparent tendency to go toward the light 

 as the cause of their movements. On thinking the results over during 

 the following winter, however, it seemed improbable that the sun's 

 rays should be the governing factor in the young turtles reaching the 

 sea, for what would happen if they were hatched on the eastern side of 

 the island when the sun was in the west? It was with the purpose of 

 finding the explanation to this question that the work was again under- 

 taken in 1908, in a much more thorough manner. I found that if several 

 young turtles were tried in Pit A when the sun was in the east, they 

 still went west. Obviously, then, they were not responding to the sun 

 in this case. Was it possible that the green bushes were the deter- 

 mining factor? If they went away from the bushes on the western side 

 of the island irrespective of whether the sun was in the east or in the 

 west, they should do so on the eastern side. Consequently, four turtles 

 were given four trials each, under the following conditions: Sun to the 

 west, bushes on the west within 8 feet of the place chosen for the experi- 

 ment (fig. I, e), which was a small, level place on the beach with a semi- 

 circular barrier of sand just high enough to shut out sight of the ocean 

 about 15 feet to the east. The turtles were tried, one at a time, by being 

 set down on the land side (west) of the barrier, headed successively to 

 west, north, south, and east. In every case, the turtles crossed the 

 barrier directly towards the sea. 



The results show conclusively that the position of the sun had 

 nothing to do with the response, but the question arose as to whether 

 or not the odor of the ocean or the sound of its waves might not have 

 been influencing factors. To obviate this I selected a spot as nearly in 

 the center of the island as possible, about an eighth of a mile from either 

 shore, where there w^as a natural semicircle of bushes inclosing a white, 

 sandy space with a definite opening into a lane, also paved with white 

 sand, on one side. At varying times of the day turtles were, one by one, 

 placed in this inclosure, headed away from the opening, and in all cases 

 (the operator, of course, being entirely out of sight) they came through 

 the opening into the space beyond with little or no hesitation. 



These experiments were further supplemented by placing green 

 glass on one side of Pit B and a number of turtles tried there, one by one. 

 In all cases they definitely and decidedly turned away from the glass 

 and climbed out of the pit on the opposite side, while in the control experi- 

 ments, where the turtles were placed in the pit when there was nothing 

 but its sandy walls for an environment, they crawled out at random 

 and went in no definite direction. 



Under ordinary circumstances the young turtles are negatively geo- 

 tropic, but if the possible descents have been exhausted, they become 

 positively geotropic. As the green bushes apparently drove them down 

 hill to the water, a series of experiments was performed to see if their 

 negative geotropism and any stimuli (if there were such) received through 

 the senses of smell and hearing from the ocean could be overcome by 

 their avoiding reaction to the green bushes. The series of experiments 



