Yerkes, space Perception of Tortoises. 25 



C. picta when blindfolded usually rushed off a surface at 

 any height without the least hesitation. There is no evidence, 

 from my experiments, that the tactual and muscular impressions 

 received when the legs are stretched over the edge have any in- 

 hibitory influence on the movement. From this it is clear that 

 the hesitation of this species observed at heights of 180 cm. is 

 due to visual impressions, not to the unusual organic impres- 

 sions received. This species at first tries to remove the cover- 

 ing from the eyes by rubbing the fore legs over the head, but 

 failing it soon becomes accustomed to the blindfolded condi- 

 tion. 



N. guttata is much disturbed by the obstruction of its 

 vision, and for long periods persistently tries to remove the cap. 

 Most individuals after a time move about freely, but whenever 

 they reach the edge of the board they turn back. Evidently 

 the tactual and muscular impressions inhibit the tendency to 

 move forward. Whereas in case of C. picta, we see the blind- 

 folded animal risking falls which it would not have risked in its 

 normal condition, in A^. guttata we see exactly the reverse, for 

 as a rule the animal when blindfolded does not leave the board. 



T. Carolina does not struggle so persistently to remove the 

 covering as do the other species, but it is inactive when blind- 

 folded. It behaves in general much as it does when placed at 

 a height of 180 cm, above the floor. This indicates that it de- 

 pends upon vision for guidance in its movements to such an 

 extent that it is not likely to move about much unless it can 

 see clearly. 



Visual impressions are of prime importance in the space 

 perception of tortoises, and tactual, muscular and organic data 

 occupy a position of secondary importance. Yet there are 

 many reasons for believing that we often underestimate the value 

 in the reactions of simple organisms of that complex mass of 

 sense impressions which we are not as yet able to refer to spe- 

 cific organs. James ('90, II, p. 150) has called attention to a 

 fact that is significant in this connection ; "Rightness and left- 

 ness, " "upness and downness, " he says, "are again pure sensa- 

 tions differing specifically from each other, and generically from 



