EVOLUTION OF INTELLIGENT BEHAVIOUR 155 
of the animal are predominantly intelligent, I am far from 
wishing to assert dogmatically that in no animals are there 
even the beginnings of a rational scheme. Indications thereof 
do not indeed at present appear to have been clearly disclosed 
by experiment. But the experimental development of the 
subject is still in its infancy. We shall probably have to await 
the further results which must be the outcome of patient and 
well-directed child-study. The human child does pass in the 
course of his individual development from intelligent to 
rational procedure. Here there is a bridge which is crossed 
by every chiid. When we know more about the stadia of this 
development we shall be in a position to apply the results 
obtained in child-study in the analogous field of animal-study. 
Till then we must possess our souls in patience, and base our 
provisional conclusions on the results of systematic investiga- 
tion, rather than on those of casual observation and anecdote. 
I1V.—THE EvouutIon oF INTELLIGENT BEHAVIOUR 
No attempt can be made in this section to trace the 
successive stages of the evolutionary progress of intelligence 
from its lower to its higher developments. It is indeed 
questionable whether comparative psychology has, as yet, 
accumulated a sufficient body of data to render such a task 
profitable or even possible. And the lower the level of 
intelligence with which we have to deal, the less reliable are 
the scanty psychological data which we can obtain. To 
interpret the mental processes which accompany the acts of 
even the higher animals is a hard task, requiring careful 
psychological analysis. Still harder is the task to infer the 
psychological basis of the actions of the lower animals. 
It is difficult to say where, in the hierarchy of animal 
progress, the beginnings of intelligence can first be traced. In 
the articulated animals, such as the insects, spiders, and 
crustacea, there is abundant evidence of intelligence of a 
relatively high grade. But even in their case, how hard it is 
