THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 157 
element of will as well as a fine example of neuro- 
muscular co-ordination. 
The study of the development of such acts as 
scratching, and that next to be referred to, are very 
suggestive and instructive to the physiologist and 
psychologist. I call special attention to this reflex 
and its psychic effects referred to in the diary on 
the 17th day, and, in the case of the Bedlington 
terriers, on the 30th day. 
WAGGING OF THE TaiL.—The tail movements of 
the dog are so expressive that the history of their 
development, and the analysis of their meaning at 
the various stages of the evolution of his life, are 
of more than ordinary interest. They are to him 
what words are to mankind. 
It is notable that I have been unable to be positive 
as to the existence of any tail movements during the 
period when the eyes are unopened, and this alone is 
significant of the relatively low state of development 
at this period. The reader is referred to the records 
OL thes Lothe i7the Ast. Zord, 28th; olst, 35th, and 
42nd days especially for notes that bear on this 
subject. 
These movements, positions, etc., of the tail have 
been to me signs of great significance, but I will leave 
the reader to draw his own conclusions. Certain it is, 
they are characteristic of certain stages of development, 
but if I were to go into full detail in reference to all 
they have suggested, this paper would become of in- 
ordinate length. It throws not a little light on this 
subject to remember that a centre for tail movements 
has been demonstrated in the cerebral cortex of the 
dog. 
SocraBiLity.—Of all animals known to us the dog 
is the most sociable. This he early indicates by his 
tail, the expression of his face, his attitudes, locomotive 
