THE EVOLUTION OF ORGANIC BEHAVIOUR 41 
likened to the inheritance of specific drafts for definite needs 
which are sure to arise in the conduct of life; the latter 
to the inheritance of a legacy which may be drawn upon for 
any purpose as occasion may demand. If the need becomes 
habitual the animal may, so to speak, instruct his banker to set 
aside a specific sum to meet it as it arises. But this arrange- 
ment is a purely individual matter, dictated by experience, and 
in no wise enjoined by the original terms of the bequest. And 
both types are fostered by natural selection which develops 
(#) such congenital definiteness of response, and (0) such 
innate plasticity, as are advantageous under the conditions 
of existence ; uniform conditions tending to emphasize the 
former, variable conditions the latter. 
Difficult as it may be to earmark the items of the organic 
bequest—to say that, of the sum of energy expended in any 
given case of organic behaviour, so much is due to a specific 
draft definitely assigned in heredity for this particular purpose, 
and so much is contributed from the general legacy of innate 
plasticity,—it none the less conduces to clear thinking to empha- 
size the logical distinction between them, so long as it is 
steadily borne in mind that logical distinction does not imply 
biological separation. The animal, with all its varied modes 
of behaviour, is an organic whole, and as an organic whole it 
has been developed from the fertilized egg. The very same 
tissues which exhibit congenital modes of behaviour are 
capable also of acquiring new responses and playing their part 
in accommodation. We have not one set of organs which are 
the products of variation and another set which result from 
modification. Our study would no doubt be simplified if this 
were the case ; but it is not so. And we must take the animal 
as we find it, presenting varied behaviour of complex origin. 
Even the reflex nervous centres, which are concerned in 
responses so automatic as to suggest a stereotyped structure of 
distinctively germinal origin, are also, as we saw at the close of 
the last section, in close touch with those centres of control 
which are associated with the supreme power of accommoda- 
tion arising from the possession of consciousness. 
