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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