640 THE BEAIN. 



rounding the optic thalami ; these parts were left in order to ensure the 

 intact condition of the latter bodies. 



When the immediate effects of the operation have passed off, and for 

 some time afterward, the appearance and behavior of the. bird are strik- 

 ingly similar to those of a bird exceedingly sleepy and stupid. It is able 

 to maintain what appears to be a completely normal posture, and can bal- 

 ance itself on one leg, after the fashion of a bird which has in a natural 

 way gone to sleep. Left alone in perfect quiet, it will remain impassive and 

 motionless for a long time. When stirred it moves, shifts its position ; and 

 then, on being left alone, returns to a natural, easy posture. Placed on its 

 side or its back it will regain its feet ; thrown into the air, it Hies with con- 

 siderable precision for some distance before it returns to rest. It frequently 

 tucks its head under its wings, and at times may be seen to clean its feath- 

 ers ; when its beak is plunged into corn, it eats. It may be induced to 

 move not only by ordinary stimuli applied to the skin, but also by sudden 

 loud sounds, or by flashes of light ; in its flight it will, though imperfectly, 

 avoid obstacles, and its various movements appear to be to a certain extent 

 guided not only by touch but also by visual impressions. 



In a certain number of cases this sleepy, drowsy condition passes off and 

 is succeeded by a phase in which the bird, apparently spontaneously, without 

 the intervention of any obvious stimulus, moves rapidly about. It does 

 not fly, that is to say, it does not raise itself from the ground in flight, but 

 walks about incessantly for a long while at a time, the periods of activity 

 alternating with periods of repose. It seems, from time to time, to wake up 

 and move about, and then to go to sleep again ; and it has been observed 

 that during the night it appears to be always asleep. It is obvious, there- 

 fore, that the sleepy, quiescent condition is not due simply to the absence 

 of the cerebral hemispheres, but is a temporary effect of the operation, and 

 that spontaneous movements, that is to say, movements not started by any 

 obvious stimulus, may occur after removal of the cerebral hemispheres. 

 But the movements so witnessed differ from those of an intact bird. They 

 are, it is true, varied ; and the variations are in part dependent on external 

 circumstances, the bird being guided by tactile, and as we have said, visual 

 sensations, or, to be more exact, by impressions made upon the sensory 

 nerves of the skin and on the retina ; but they do not show the wide varia- 

 tions of voluntary movements. The bird never flies up from the ground, 

 never spontaneously picks up corn, and its aimless, monotonous, restless 

 walks, resembling the continuous swimming of the frog thrown into the 

 water after being deprived of its cerebral hemispheres, forcibly suggest that 

 the activity is the outcome of some intrinsic impulse generated in the 

 nervous machinery in some way or other, but not by the working of a con- 

 scious intelligence as in the impulse which we call the will. 



Still we must not shut our eyes to the fact that spontaneous movements, 

 whatever their exact nature, are manifested by a bird in the absence of the 

 cerebral hemispheres, and become the more striking the more complete the 

 recovery from the passing effects of the mere operation. Could such birds 

 be kept alive for any considerable time, possibly further developments 

 might be witnessed, and indeed cases are on record where birds have been 

 kept alive for months after the operation, and have shown spontaneous 

 movements of a still more varied character than those just described ; but 

 in such cases the removal of the hemispheres has not been complete, por- 

 tions of the ventral regions being left behind ; and, though a mere remnant 

 left around the optic thalami can hardly be regarded as a sufficient cause 

 for the spontaneity of which we are speaking, a larger mass, still more or 

 less retaining its normal structure, might have a marked effect. And we 



