172 INTELLIGENT BEHAVIOUR 
We have already seen that instinctive behaviour is primarily 
a matter of the first occasion on which any given action is 
performed, and that many instinctive acts are subject to sub- 
sequent modification in the light of the experience gained 
during the early performances. The range of such modification 
varies both in different animals and also with respect to 
different modes of behaviour in the same animal. The more 
fixed and deeply rooted an instinct the less readily does 
intelligence obtain a hold on it, so as to direct the behaviour 
into new channels of better accommodation to the circum- 
stances. M. Fabre describes how a Sphex, one of the solitary 
wasps, instinctively draws its prey, a grasshopper, into the 
burrow by its antenne. When these were cut off the wasp 
pulled the grasshopper in by the jaw appendages ; but when 
these were removed she seemed incapable of further accom- 
modation to the unusual circumstances. It would seem an 
easy and obvious application of intelligence to seize the prey by 
one of the forelegs. But this was not done; and the grass- 
hopper was then left. Intelligence did not seem equal to 
meeting the altered conditions presented by the maimed grass- 
hopper. Still, there was some modification of the normal 
instinctive behaviour ; and, as Dr. Peckham has shown, there 
may be more than Fabre noted. Let us assume the exist- 
ence of an animal whose every act is instinctive, whose 
whole behaviour is marked out in strictly hereditary lines, no 
new departures being acquired in the course of individual life. 
This extreme case would afford an example of what we may 
term completely stereotyped behaviour. On the other hand, let 
us assume the existence of an animal with no _ hereditary 
definiteness of reaction, whose every act is intelligent, whose 
whole behaviour is the result of individual acquisition. This 
antithetical extreme case would afford an example of what we 
may term completely plastic behaviour. It is questionable, 
however, whether either of these extreme types occur in nature. 
What we find in our study of animal behaviour is some inter- 
mediate condition in which both factors co-operate, with a 
predominance either of stereotyped instinctive response on the 
