THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 155 
scarcely to be recognised. The ear, in fact, grows and 
differentiates after birth in somewhat the same way 
as the eyelids, but the latter are invariably in advance, 
so that there are physical reasons for the deafness of 
puppies. Even after the ear seems to be opened up, 
the introduction of a fine probe is impossible, as I have 
shown. 
Psychic manifestations may be looked at from so 
many different points of view, and the correct inter- 
pretation is so often doubtful, especially in the lower 
animals, one’s explanations are apt to be so artificial, 
narrow, or otherwise imperfect, that I shall, under 
several headings, now refer to the early development 
of the puppy. 
Pray.—I have endeavoured to follow very closely 
the development of the play instinct, so important is it 
as a means of physical and psychic development, as 
well as an indication and an index of the latter—in fact 
of both. The reader is referred to records of the 13th, 
15th, 21st, 27th, and 32nd days more especially. I 
have felt keenly my inability to record all that I have 
seen in this connection, not to mention the thoughts 
suggested, which lack of space prevents me making 
even an attempt to indicate. 
What is play? One observes, first of all, that the 
puppy uses its mouth generally on a fellow, then, or 
simultaneously, its paws; but soon the movements 
are more complicated, prolonged, and accompanied by 
various vocal expressions, which are of a significance 
which varies with the age of the puppy. 
There is not the slightest attempt at play during 
the period of eye-closure. 
At first, playing seems to arise in part from an 
excess of motor energy which must be discharged, 
and as it is in the nature of the dog to use his jaws 
so much, the play takes the special form of biting ; then 
