610 THE BRAINLESS FROG. [BOOK m. 



bodily movement by throwing into activity particular parts of the 

 nervous machinery situated in the lower encephalic structures; 

 and precisely the same movement may be initiated in their 

 absence, by applying such stimuli as shall throw precisely the same 

 parts of that machinery into the same activity. 



Very marked is the contrast between a frog which, though de- 

 prived of its cerebral hemispheres, still retains the optic lobes, cere- 

 bellum and medulla oblongata, and one which possesses a spinal 

 cord only. The latter when placed on its back makes no attempt 

 to regain its normal position ; in fact, it may be said to have com- 

 pletely lost its normal position, for even when placed on its feet it 

 does not stand with its fore feet erect, as does the other animal, 

 but lies flat on the ground. When thrown into water, instead of 

 swimming it sinks like a lump of lead. When pinched, or other- 

 wise stimulated, -it does not crawl or leap forwards ; it simply 

 throws out its limbs in various ways. When its flanks are stroked 

 it does not croak ; and when a board on which it is placed is 

 inclined sufficiently to displace its centre of gravity it makes no 

 effort to regain its balance, but falls off the board like a lifeless 

 mass. Though, as we have seen, there is in all parts of the spinal 

 cord of the frog a large amount of coordinating machinery, it is 

 evident that a great deal of the more complex machinery of this 

 kind, especially all that which has to deal with the body as a 

 whole, and all that which is concerned with equilibrium and is 

 specially governed by the higher senses, is seated not in the spinal 

 cord but in the brain including the medulla oblongata; and 

 apparently a great deal of this more complex machinery is con- 

 centrated in the optic lobes. The point however to which we wish 

 now to call special attention is that the nervous machinery re- 

 quired for the execution, as distinguished from the origination, of 

 bodily movements even of the most complicated kind, is present 

 after complete removal of the cerebral hemispheres, though these 

 movements are such as to require the cooperation of highly 

 differentiated afferent impulses. 



Our knowledge of the phenomena presented by the bird or 

 mammal from which the cerebral hemispheres have been removed 

 is not so exact as in the case of the frog. Under such circum- 

 stances movements apparently spontaneous in character are more 

 common with the bird or mammal than with the frog. This 

 might be expected, seeing that the more complicated brain of the 

 former affords, even in the absence of the cerebral hemispheres, 

 much more opportunity for the origination of stimuli within the 

 nervous system itself, and for the play of stimuli however origi- 

 nating, than does that of the latter. It would be hazardous to 

 regard such apparently spontaneous movements as indications of 

 volition, and indeed it seems a priori improbable that the will 

 should be confined to the cerebral hemispheres in the frog, and yet 

 so to speak diffused among other parts of the brain in the more 



