The Making of Species 
which in their turn are built up of biological 
radicles and atoms. These behave in some ways 
like chemical molecules, radicles, and atoms, as 
the case may be. 
It seems legitimate to regard each unit char- 
acter in the adult as the result of the develop- 
ment of one or more of the biological molecules 
which compose the nucleus of the fertilised egg. 
These biological molecules are, of course, a 
million-fold more complex than chemical mole- 
cules. Each biological atom must contain within 
itself a number of the very complex protoplasmic 
molecules. This view of the structure of the 
germ cell seems to force itself upon the observer. 
Notwithstanding this, the conception will have no 
value unless it seems to throw light on the various 
phenomena of heredity, variation, etc. 
Let us then try to interpret some of these. 
Each chemical element is made up of atoms 
which are all of the same kind, but no two 
elements are made up of the same kind of atoms, 
although chemists are now inclined to conceive of 
all the various kinds of atoms as made up of 
varying amounts of some primordial substance. 
In any case, the molecules of chemical compounds 
are made up of various kinds of atoms. With 
biological atoms the case would seem to be 
different. All would appear to be made up of 
the same kind of substance, and the differences 
shown by the various unit characters that go to 
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