Variation as an Organic Function 163 
it may or may not be more than the mere summation of such a 
series. It is a unity , co-ordinated in time and space, that has definite 
form and direction. Thus in every organism cell-division constitutes 
a primary activity. It is a type of organismal behaviour that we 
can recognise as being at once generally constant and qualitatively 
distinct, although we cannot at present give it any interpretation in 
physiological terms. 
Cell-division is, however, by no means an isolated or sporadic 
phenomenon. In the process of ontogeny beginning with the first 
segmentation of the zygote, the successions of cell-divisions are co¬ 
ordinated in a number of parallel but interdependent sequences 
which give rise to the somatic morphological characters at every 
stage of development. The character of these sequences, and the way 
in which they are mutually related are also fundamental aspects of 
the organic activity-system. 
As a somewhat more complex example, functional adaptation is 
a distinct type of activity. When for instance we observe that a 
plant responds to an increase in the intensity of sunlight by a variety 
of distinct and apparently co-ordinated bodily movements having 
the effect of reducing transpiration, we simply recognise certain 
changes in the environment-state of a particular familiar quality. 
In the same way, in the higher organisms, instinctive and intelligent 
behaviour are distinct types of activity. Their psychological aspect, 
as inferred by analogy with our own subjective experience, does not 
primarily concern the biologist qua biologist. From the biological 
standpoint instinctive and intelligent acts are essentially a part of 
the process of somatic development, differing only qualitatively from 
cell-division, tissue-differentiation, and internal bodily readjustments 
that are the normal accompaniment of every individual life. There 
is however the important difference that the environmental changes 
by which these higher activities are recognised and defined are for 
the most part external to the body of the organism in the ordinary 
sense. In this category we should place not only co-ordinated bodily 
movements, but also the various external structures which result 
from the instinctive and intelligent behaviour of the higher animals, 
such as the web of a spider, the mud cells of the mason bee, the nest 
of a bird, the lodge of a beaver, or even a machine constructed by 
man. These “external characters” are essentially a part of the 
organism’s morphological structure, and the energy-reactions with 
which they are associated are an integral part of its physiological 
economy. They are definitely specific, and may, or may not, show a 
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