THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 275 
V.—BiIrDs. 
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 
