INTRODUCTION. 
8 
that the lower down we go in the animal kingdom, the 
more we observe reflex action, or non-mental adjustment, 
to predominate over volitional action, or mental adjust- 
ment. That is to say, the lower down we go in the 
animal kingdom, the less capacity do we find for changing 
adjustive movements in correspondence with changed 
conditions ; it becomes more and more hopeless to teach 
animals — that is, to establish associations of ideas; and 
the reason of this, of course, is that ideas or mental units 
become fewer and less definite the lower we descend 
through the structure of mind 
It is not my object in the present work to enter upon 
any analysis of the operations of mind, as this will require 
to be done as fully as possible in my next work. Never- 
theless, a few words must here be said with regard to the 
main divisions of mental operation, in order to define 
closely the meanings which I shall attach to certain terms 
relating to these divisions, and the use of which I cannot 
avoid. 
The terms sensation, perception, emotion, and volition 
need not here be considered. I shall use them in their 
ordinary psychological significations ; and although I 
shall subsequently have to analyse each of the organic or 
mental states which they respectively denote, there will 
be no occasion in the present volume to enter upon this 
subject. I may, however, point out one general con- 
sideration to which I shall throughout adhere. Taking 
it for granted that the external indications of mental 
processes which we observe in animals are trustworthy, so 
that we are justified in inferring particular mental states 
from particular bodily actions, it follows that in con- 
sistency we must, everywhere apply the same criteria. 
For instance, if we find a dog or a monkey exhibiting 
marked expressions of affection, sympathy, jealousy, rage, 
<fec., few persons are sceptical enough to doubt that the 
complete analogy which these expressions afford with 
in either case ; but this is the side issue which concerns the general 
relation of body and mind, and has nothing to do with the guarantee 
of inferring the presence of mind in particular cases. 
