IIo , INSTINCTIVE BEHAVIOUR 
have already seen, modern investigation has placed this matter 
of so-called hereditary fear of natural enemies on a different 
footing. Pheasants, partridges, moor-hens, and wild duck show 
no fear of a quiet dog. If approached gently, in the absence 
of their parents, callow wild birds in their nest exhibit little 
alarm at the slow and gentle approach of man. Mr. Hudson’s 
opinion has already been quoted, but will bear repetition ; it 
is, “that fear of particular enemies is in nearly all cases the 
result of experience.” And there is no evidence to show that, 
in those cases in which it is truly instinctive and not the result 
of experience, the instinctive behaviour is necessarily due to 
inherited habit and not to natural selection. 
It cannot be said that the evidence for the supposed mode 
of origin of secondary instincts is sufficiently varied and cogent 
to carry conviction. On the other hand, there does seem 
some evidence which points to a different conclusion. When 
instinctive behaviour follows on a sensory impression, not only 
is the co-ordination hereditary, but there is an inherited link- 
age of stimulus and response. Thus in the solitary wasps the 
sight of the natural prey is followed by the appropriate modes 
of attack. The J/e/oé larva springs upon anything hairy. In 
chicks the sight of a small object at a certain distance initiates 
the act of pecking. In moor-hens and ducklings the stimulus 
of water produces the movements concerned in swimming. 
And so, too, in many other examples of instinctive behaviour, 
we infer from the observed facts that stimulus and response 
have an organic connection founded on hereditary links in the 
nervoussystem. Now, if such connection were due to inherited 
habit, we should expect them to be established wherever the 
experience to which they are related has been constant through 
wavy generations. How comes it, then, that the chick does 
not instinctively respond by appropriate behaviour to the 
sight of water? How comes it that young birds do not 
instinctively avoid bees, and wasps, and nauseous caterpillars ? 
If the effects of ancestral experience be hereditary, one would 
surely expect that in these cases the connection between 
stimulus and response—a connection which passes into acquired 
