22 /oiimal of Comparative Neurology aiid Psychology. 



tial relations are concerned, and the behavior of the animals. 

 A land tortoise has cause to notice heights and to react to them 

 in a manner different from that of a water form. The former 

 plunges over a precipice and is dashed to pieces, the latter 

 plunges into the water from an equal height without injury. 

 It is interesting to note, too, that there are intermediate forms 

 between the two extremes, for the "spotted" tortoise N. gut- 

 tata is more careful in its reactions to space than C. picta, but 

 less so than T. Carolina. 



We may now turn from the roughly quantitative facts of 

 this study to the observations of the general behavior of the 

 animals when placed in unusual spatial conditions. 



Of the three species of tortoises under consideration 

 Chrysemys picta is the most active. At a height of 30 cm. it 

 usually plunges off without hesitation ; at 90 cm. it frequently 

 stops at the edge, looks about carefully, and sometimes draws 

 back and seeks another part of the edge. There can be no 

 doubt that it senses the spatial relations in visual terms. At 

 180 cm. this species is manifestly afraid of the edge. Some in- 

 dividuals hesitate for long intervals before pushing off into 

 space ; others rush off at once. Usually, however, at this 

 height the edge of the board is carefully explored, and abortive 

 attempts to push off are made repeatedly. There is no evidence 

 that the unusual conditions are perceived until the animal 

 reaches the edge of the board. 



Naneinys guttata hesitates even at the height of 30 cm. 

 Most individuals carefully examine the board and look intently 

 toward the net and surrounding objects before pushing off. 

 They crane the neck over the edge to a greater e.Ktent than does 

 C. picta. When 90 cm. or more above the net this species sel- 

 dom approaches the edge without manifestations of fear. Fre- 

 quently an individual pushes itself almost over, then stops sud- 

 denly and draws back, or attempts to catch the edge with its 

 claws to save itself from falling. This striking conflict of im- 

 pulses sometimes occurs repeatedly before the animal finally goes 

 over the edge. The tortoise is impelled by the narrowness of 

 its confines on the board, and by its isolated and exposed posi- 



