170 ANIMAL INTELLIGENCE 
While the puppy sprawls in the blind period, he cannot 
investigate objects, and we find, as the sensory organs 
advance in development, the animal’s locomotor power 
increases, so that he can the better use all his senses, 
hence the great strides he makes in development from 
one part undergoing a change which adapts it to the 
well-being of other parts and the entire organism. 
As a matter of fact, motor power is, in the young 
animal, a very fair guide to its general advancement, 
and in tracing the development of the puppy one notices 
this daily. 
There is a certain order of progress: first the tongue 
laps, etc.,as in sucking; then after the eruption of 
teeth, use of the jaws at the same time; and more so 
later the movements of the fore-limb—long, in fact 
always, in advance of the hind-limb—the tail soon 
taking a share in the movements. 
These movements not only increase in power, but in 
precision, 7.e. they are co-ordinated, and this is well 
illustrated by many facts stated in the diary. 
These movements, the development of the senses, 
etc., etc., are of course impossible without the nervous 
system, and they gain in precision and variety, accord- 
ing to the rate and extent to which the cortex of the 
cerebrum is developed into functional activity. My 
own experiments on the brains of young animals are 
not yet complete, so that I shall not here refer to them 
further than to state that they bear out the view just 
stated. During the blind period the cerebral cortex is 
found to be unexcitable, while in the mature dog move- 
ments of definite groups of muscles may be readily 
obtained by stimulation of the cortex. 
DIFFERENCES IN BreEEDS.— Both physically and 
psychically there are differences in development in 
the various breeds of dogs. 
I found that the litter of Bedlington terriers 
