114 PARKER— THE RELATIONS OF THE 



in which food is hidden, they begin sweeping the bottom in rapid 

 circular movements, turning now to the right and now to the left. 

 If both nostrils in the fish are closed with plugs of cotton, these 

 movements do not occur. If, now, one nostril is freed, the circular 

 form of locomotion returns with this peculiarity, however, that the 

 circles are now almost always in one direction — i.e., with the free 

 nostril toward the center. Plainly the dogfish scents its food and in 

 hunting turns, as animals exhibiting tropisms do, in the direction 

 appropriate for the more intense stimulus. Thus the dogfish shows 

 responses that in every way have the earmarks of a tropism. This 

 condition, however, is very exceptional, for in general the responses 

 of vertebrates to their environment, as every one knows, resemble 

 vastly more those of the more complex insects than they do the tropic 

 reactions of the simpler organisms. 



A remarkable form of vertebrate response in this particular is the 

 instinct shown by newly hatched loggerhead turtles to go toward the 

 ocean. It is a most singular spectacle to see a dozen or more of these 

 newly hatched creatures scramble across the horizontal surface of a 

 wharf directly toward the water which, in consequence of a raised 

 wooden edge, they could not see and with which they had had no 

 previous experience. What determined their direction of motion was 

 at first sight very difficult to say. After some trials, however, it was 

 found that they commonly went away from any large diversified mass, 

 especially when it occupied a part of the horizon line, and they as 

 commonly went toward a uniform and uninterrupted part of the 

 same line. Their first steps in this operation were extremely inter- 

 esting to watch. When a young turtle is placed in position to move, 

 he quickly raises his head, makes a complete turn through a whole 

 circle to test out apparently his surroundings, and then takes a 

 straight course toward the clearest part of the horizon. That this 

 reaction has of necessity nothing whatever to do with the ocean can 

 be shown by starting the turtle near some high shrubbery, but on the 

 side away from the sea and toward a free, open field. The animal 

 will then move away from the shrubbery and toward the open field 

 with as much certainty as it had previously done toward the water, 

 though in this instance it is plainly moving away from the element 

 which ordinarily it would be expected to seek. 



