THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 275 



V, BIRDS. 



ONE learns how large a proportion of the possibilities, 

 physiological if not psychic, in the pigeon are not 

 dependent on the cerebral cortex, or even the entire 

 cerebrum, by ablation of the latter. Movements, 

 though not spontaneous, are nearly as perfect afterwards 

 as before, and much light is thrown on the nature of 

 reflexes. 



I have, after careful investigation, been unable to 

 find any motor cortical centres whatever. The whole 

 cerebral cortex appears to be absolutely inexcitable, 

 except, perhaps, as concerns certain eye movements, 

 and as for these a strong stimulus is required, it is 

 doubtful if they are of cortical origin in the usual sense 

 of the term. 



Nevertheless, unless we deny the existence of 

 voluntary movements to the bird an extreme position 

 we are landed in physiological difficulties, inasmuch 

 as it has been assumed by nearly all physiologists that 

 the cortex is essential to voluntary movements. The 

 case of the bird seems to me to show that we have 

 much to learn as to the nervous mechanism of 

 voluntary movements, notwithstanding all the in- 

 vestigation that has been given to this subject. 



Conclusions. 



In the dog and the cat there is a period, extending 

 from birth to about the time of the opening of the eyes, 

 characterised by reflex movements, the sway of instincts, 

 and the absence of intelligence. During this time the 

 cerebral cortex is inexcitable by electrical stimulation, 

 so that the psychic condition during the blind period is 

 correlated with an undeveloped state of the motor 



