168 ANIMAL INTELLIGENCE 
hear, and the same animal ten days afterwards, there is 
indeed a vast difference. But as to the rate and nature 
of development the reader may draw his own con- 
clusions, and to enable him to do so has been my chief 
object in giving a record of facts so detailed and as free 
from gaps and omissions as possible. I am convinced, 
moreover, that the whole difference in the periods referred 
to is not to be referred merely to the presence or absence 
of vision and hearing. 
About this time the whole nature of the animal seems 
to undergo a comparatively sudden leap forward in 
advancement, possibly as the result of the accumulated 
experiences of ages acting through heredity—I mean 
that the advances directly referable to the advent of 
seeing and hearing would tend to accumulate by 
heredity, and to be expressed in the organism in time 
in a more decided manner. 
GENERAL.—The preceding are a few of the many 
aspects of the psychic (and physical) development pre- 
sented within the first sixty days of existence of puppies. 
I deprecate hard and fast lines of demarcation in biology 
and psychology, believing that in nature one thing, as a 
rule, glides into another at some stage of development, at 
all events. My commentary on the diary is, therefore, 
not claimed to be complete, if indeed it is possible 
to recognise all that there is in psychic development, 
however closely one may observe, however perfectly 
analyse. 
PHYSICAL CoRRELATION.—Already, for some years, the 
relations of mind and body have been recognised in a 
general way, and studied with results of definite value ; 
but while there have been isolated experiments and 
observations made on young animals bearing on the 
relation between physical development and the psychic 
status, I am not aware that any complete and systematic 
study of the subject has been attempted. That the mind 
