SPACE PERCEPTION OF TORTOISES. 

 By Robert M. Yerkes. 



{From the Harvard Psychological Laboratory, HuGO MtTNSTERBKRG, Director.) 



The Sense of Support in Animals. 



A number of investigators have noticed that the young of 

 many animals possess a sense of support, and that their behavior 

 is adapted to the spatial conditions in which they happen to be 

 placed. It is this sense of support that saves the sightless kit- 

 ten or puppy from falls ; but in case of the young chick which 

 similarly hesitates when it approaches the edge of a void visual 

 stimuli apparently determine the reaction. These reactions to 

 spatial conditions are controlled by a complex of sense impres- 

 sions which is still unanalyzed. In certain animals visual im- 

 pressions seem to be all-important ; in others organic data are 

 chiefly significant, and again in other organisms there are indi- 

 cations of degrees of sensitiveness, if not modes of sense, of 

 which we have no direct knowledge. And so, strange as it 

 may seem, the "spatial worth" of sense data, as James would call 

 it, is no more a matter of accurate knowledge than is the de- 

 velopment of the sense of space, or the modes of behavior in 

 different spatial conditions exhibited by any animal. 



Thorndike ('99, p. 284), who has studied the behavior 

 of young chicks with reference to spatial relations, says "If 

 one puts a chick on top of a box in sight of his fellows below, 

 the chick will regulate his conduct by the height of the box." 

 A chick 95 hours old does not hesitate to jump off at heights 

 of I to 10 inches; at 22 inches it often hesitates a long time, 

 and at 39 inches it usually does not jump at all. Furthermore, 

 immediately after hatching, young chicks are able to peck at 

 objects with considerable accuracy, and they apparently esti- 

 mate distances fairly well before they have had much experience 

 outside the shell. 



