Yerkes, space Perception of Tortoises. 19 



of this sense (the sense of support) is unmistakable, and is not 

 due to experience, as I have found by trying rats that have had 

 no such experience." And Watson ('03, p. 40) remarks that 

 a rat that wanted to get down from the top of the food box 

 "would usually stretch his head down two or three times, then 

 pull himself back, as though he feared to attempt such a dan- 

 gerous a feat." 



The observations quoted indicate the possibility of inter- 

 esting studies of the development of space perception in animals, 

 and of such analyses of the sensory complex as shall exhibit 

 the 'spatial worth' of each kind of sense data. Partly for the 

 purpose of making an approach to the comparative study of 

 space perception, partly for the solution of the following specific 

 problems I have observed the behavior of several species of tor- 

 toises with respect to spacial conditions. The question which 

 really led to the investigation was, What relation do the reac- 

 tions of tortoises to space bear to their habits ? Does the water 

 species behave in essentially the same manner as does the land- 

 inhabiting form ? The attempt to answer this question led to 

 the study of the general behavior of different species, and of the 

 importance of vision and the 'sense of support' in reactions to 

 space. 



Relation of Reactions to Space to Habits in Tortoises. 



My method of experimentation was to place a tortoise in 

 the middle of a board 30 cm. by 60 cm. which was elevated 

 30 cm., 90 cm. or 180 cm. above a net of black cloth into which 

 the animal fell when it crawled or plunged over the edge of the 

 board. The fall was thus rendered harmless to the animals, 

 and they gave no evidence, by increased hesitancy in crawling 

 off, that it was disagreeable to them. The observer carefully 

 noted the behavior of the tortoise while it was on the board, 

 and recorded the time that it remained there. It would seem 

 that the time from the noticing of the edge of the board till the fall 

 should be recorded rather than the total time spent on the board, 

 but as it was found that some species notice the spatial condi- 

 tions while they are still in the middle of the board, whereas 



