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greater range of individual fluctuation than the ordinary bodily 
characters to which the biologist customarily confines himself. 
This difference between internal and external characters necessi¬ 
tates, however, that we should define the sense in which we use the 
term "environment” a little more precisely. It is proposed to retain 
the distinction between the unspecialised primary environment out¬ 
side the organism, and the specialised secondary environment which 
comprises all the matter within the sphere of its activities. In plants 
the secondary environment will be practically all included within the 
morphological body. In the much more complex case of an insect 
colony however, it will also include all material structures associated 
with the life of the colony that have resulted from environmental 
changes brought about by the activities of the individual insects, 
such as the nest, cocoon-cases, and external food supplies. 
Activities are thus seen to be definite aspects of the life of the 
organism of which we have an empirical knowledge. They are events 
in the phenomenal world having properties of their own, that place 
them in a unique category. Even if it be ultimately true that an 
activity is only a sequence of energy-reactions physically determined, 
the more empirical method of investigating biological problems 
advocated here has at least the advantage that it enables us to deal 
more readily with very complex phenomena by utilising the fact 
that we find certain natural groupings ready to hand. It may be, of 
course, that this method will afford only approximations to the 
truth, whereas a fuller and more accurate interpretation of life 
processes could be given by a complete physiological knowledge. 
But as there is at present no possibility of such a complete physio¬ 
logical knowledge, it may be legitimate and useful to employ more 
empirical data as the basis of a provisional hypothesis. 
The relation of this view of biological phenomena to the ordinary 
conception of structure and function is a simple one. At any moment 
in the organism’s life there is present a certain definite environmental 
configuration. This consists of a number of elements, some of which 
are primary (air, light, water and other organisms), and some 
secondary, i.e. having special qualities or dispositions resulting from 
the past activities of the organism in question. A structural character, 
such as a tracheid of a plant, is a group of secondary environmental 
factors that remain relatively constant during an appreciable period. 
The function of such a structure (in this case water-conduction) is a 
persistent type of energy-reaction in which those particular environ¬ 
mental factors are involved. As a somewhat different illustration, 
