CEREBRAL HEMISPHERES AND MEMORY 237 



hemispheres, which produces so great a change in the 

 personality of a higher animal, has much less effect on 

 a froe. In the shark, nothing in the habits or reac- 



^5 O 



tions of the normal animal shows the existence of 

 associative memory. Most of its reactions are inher- 

 ited and composed of segmental reflexes. We find, 

 correspondingly, that it shows very little change after 

 the extirpation of the cerebral hemispheres, for in 

 spite of their loss the segmental reflexes are pre- 

 served. 



It would be a mistake to assume that the loss of the 

 cerebral hemispheres in no way affects the animal. 

 Its loss has a certain effect upon the segmental re- 

 flexes. Nereis has no associative memory, yet it shows 

 a certain lack of inhibition after the loss of the supra- 

 cesophageal ganglion (see Chapter VI.). Something 

 similar is noticeable in lower Vertebrates whose cere- 

 bral hemispheres are removed. For instance, in ad- 

 ders all segmental reflexes are preserved after loss of 

 the cerebral hemispheres. Schrader found, however, 

 that such animals no longer show any " fear " -it was 

 not possible to frighten them although all the opticus- 

 reflexes still functioned (2). From this we must con- 

 clude that the effects of those stimuli which extend 

 from the opticus-segment into the central nervous 

 system are different, so long as the cerebral hemi- 

 spheres exist, from what they are when the hemi- 

 spheres have been extirpated. Something of this 

 kind also shows itself in the frog. Goltz has found 

 that the frog without cerebral hemispheres is better 



