Biological Molecules 
white dress, is (although the change is from 
brown to white) again conducted along precisely 
similar lines.” Mr Bonhote argues with great 
force that, as the process occurs in two animals 
so widely separated, the fundamental cause must 
be a deep-seated one. There can be no doubt 
that these pcecilomeres of Bonhote are connected 
with our biological molecules. Each of these 
pecilomeres is the result of the development 
of one of these unit characters; each is to be 
regarded as the centre of activity, the sphere of 
influence of a biological molecule, or the portion 
of one, which controls the colouring of a definite 
region of the organism. In the case of creatures 
which display the same colour throughout, these 
molecules all give rise to the same kind of 
colouring ; in the case of animals which display 
a variety of colours and markings the various 
molecules give origin to various colours. But 
we must bear in mind that the final colour to 
which each colour-producing molecule gives rise 
depends to some extent on circumstances other 
than the constitution of the molecule. Thus it 
is that the young in most organisms differ in 
colour and marking from the adults. On this 
also depends the phenomena of seasonal and 
sexual dimorphism. The same colour-producing 
molecule may give rise to one colour under one 
set of conditions and to a totally different colour 
under another set of conditions. 
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