CEREBRAL HEMISPHERES AND MEMORY 243 



It does not learn this reaction any more than a plant 

 learns its heliotropic reactions, and it is no more 

 necessary for the suckling than for the chick to learn 

 space-reactions. They come " of themselves " as soon 

 as the embryonic development of the suckling has ad- 

 vanced far enough. This conception, to which com- 

 parative physiology forces us, is further supported 

 most effectually by Schrader's observation (and by 

 those of earlier authors, for instance, Longet) that 

 visual space-perception in birds continues after the 

 cerebral hemispheres have been removed. The pos- 

 sibility that this holds good for birds and not for 

 mammals is refuted by a statement of Christian! in 

 regard to rabbits. The fact, however, that space- 

 reactions can be modified by the memory, that we 

 can " learn " to shave before a mirror, for instance, 

 or can " learn " to grasp things in spite of prismatic 

 glasses, does not contradict this conception any more 

 than the acquired accomplishments of the dancer con- 

 tradict the fact that normal walking is not a matter 

 of memory. The fact that coordinated progressive 

 movements on the turn-table occur in the direction of 

 the plane of the rotation, and those produced by a gal- 

 vanic current occur in the direction of the curves of 

 the current, also speaks for this nativistic conception. 

 From this digression we will now return to Schra- 



o 



der's experiments. The pigeon described above as 

 wandering about the room all day, sleeps at night. 

 Sleep has nothing to do with consciousness and mem- 

 ory, for it occurs in plants. It is not surprising then 



