spatially Determined Reaction 237 



That carrier pigeons depend on visual landmarks is main- 

 tained by many authorities. They do not fly at night, 

 nor do they home well in cloudy weather. Young pigeons 

 have to be trained on short distance flights, though of 

 course this might be the case if they depended on some 

 other power than recognition of visual landmarks. Mi- 

 grating birds in some cases fly long distances over the ocean, 

 where no visual clues can be furnished. Watson (769) 

 caused some noddy and sooty terns to be carried in a steamer 

 from the Tortugas Islands to the latitude of Cape Hatteras, 

 a distance of nearly a thousand miles, where they were 

 liberated. The locality is far out of their range of habitat, 

 yet they returned to their breeding place in about a week. 

 Hachet-Souplet ^ suggests that a very vague visual image, 

 of objects too far off to be clearly seen, may be used 

 in such long distance homing, but the curvature of the 

 earth would interfere with a bird's getting even a vague 

 image of any surroundings that could be famiUar to it. 



§ 69. Class V : Reactions adapted to the Distance of Objects 



The factors that make possible the perception of the 

 third dimension, depth, or distance outward from the body, 

 in invertebrate animals are little known. Certain inverte- 

 brates do give evidence of • the power to judge distance. 

 The hunting spiders, for example, which do not make webs, 

 but pursue their prey in the open, leap on it from a distance 

 of several inches. Dahl thinks their distinct vision is limited 

 to two centimeters (168), and Plateau says capture is 

 not attempted until the prey is within this distance (596). 

 The Peckhams, however, tested a hAnting spider by putting 



' VI CongrSs Int. de Psychologie, 1909, p. 663. I have been unable to 

 obtain the original article. 



