THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 269 
which they are reflex, or according to the facility with 
which higher centres use lower ones, and thus economise 
psychic energy. 
But even so early as the 12th to the 15th day 
new movements are possible. The eyes have opened, 
the ears also, and both eyes and ears move, rather 
reflexly at first beyond doubt, but very soon the puppy 
moves both eyes and ears voluntarily at times, and 
still later he fixes the eyes, which is clearly a voluntary 
act. 
It is obvious that there is now an approach to walk- 
ing (instead of crawling), There are tail movements 
by the 17th day, and the scratching reflex is excitable. 
The tail movements are, at this period, almost certainly 
reflex. Voluntary movements of the tail do not seem 
to be possible till a good deal later, which corresponds 
with the well-established fact that the cortical centre 
for tail movements is not developed till comparatively 
late. 
The barking of the 19th day was probably a reflex, 
much simpler than such as results later. At this stage, 
puppies often bark in their sleep, not a common occur- 
rence with mature dogs, though it does take place in 
dreaming. By the 25rd day, the puppies stand with 
the paws on the edges of the boards constituting the 
walls of their pen. This act may be reflex at times, 
possibly, but on other occasions it is clearly voluntary, 
and, as they try to get out, we are left in no doubt that 
they are capable of willed movements, so that by this 
time, and probably before, there are undoubted volun- 
tary movements. Corresponding with this advance, 
I have found before the 20th day very distinct cortical 
localisation for the limbs, head, and face. 
Later than this, improvement in reflexes is noticeable, 
but still more the rapid development of older and the 
