spatially Determined Reaction 239 



When, however, the mice were required to judge which of 

 two partitions was nearer to their startingTpoint, and to 

 turn to the right or the left in accordance with this pre- 

 liminary judgment in returning to their nest, they failed : 

 this really involves a rather complex type of learning, and 

 is a much less fair test of the mere ability to perceive dis- 

 tance than is the instinctive reaction of jumping. In 

 Richardson's (634) study of the rat, the animals were 

 trained to jump from one horizontal support to another. 

 They proved able to judge quite accurately the direction 

 of the platform to which they had to jump, but when its 

 distance was altered they could not adapt themselves, 

 and jumped either too far or too short. 



Yerkes's tests of the so-called 'sense of support' in tor- 

 toises indicate, like Waugh's experiments on the mouse, 

 some power of estimating distance by vision in these ani- 

 mals. He experimented, it will be remembered, with 

 individuals belonging to three classes : land-dwelling, 

 water-dwelhng, and amphibious. The first mentioned 

 would crawl off the edge of a board 30 centimeters above 

 a net of black cloth only with much reluctance when their 

 eyes were uncovered; when bhndfolded they would not 

 move at all. The water tortoises plunged off without 

 hesitation from a height of 30 centimeters, but hesitated 

 sUghtly at 90 centimeters, although some individuals 

 would take the plunge at once even from a height of 180 

 centimeters. When bhndfplded, all of the water tortoises 

 rushed off at any height. The land-and-water-dweUing 

 tortoises hesitated at 30 centimeters and at 90 centimeters 

 showed a conflict of impulses, trying to catch themselves 

 before launching off. When blindfolded they would not 

 leave the board at all, though they moved about upon it 

 freely (810). 



