SYMMETRY 129 
{2) that such a form of variation is by no means so 
uncommon a phenomenon as was formerly supposed ; 
and (3) that variations of this kind may occur in 
every description of organ and part in a number of 
different plants and animals. The facts with which 
the main bulk of the book is concerned have reference 
to the animal kingdom. 
We shall find it profitable to consider the views 
expressed in this book a little more closely, though it 
would occupy too much space to give even a brief 
summary of the facts upon which they are based, and 
for which reference must be made to the original. 
In the first place Bateson calls attention to the 
phenomenon of symmetry as being a characteristic 
feature common to almost all organisms. This sym- 
metry may manifest itself in a number of different 
ways. In bilateral and radial symmetry the parts 
symmetrically disposed are related to one another in 
the same kind of way as are an object and its image 
reflected in a plane mirror. Such symmetry, as, 
indeed, every kind of symmetry, is usually associated 
with a repetition of parts. In the present instances 
the parts are repeated in pairs, as with the two eyes 
in the human face ; or in a radial series, like the arms 
of a star-fish, or the petals of a buttercup. To this 
phenomenon of the repetition of parts, generally 
occurring in such a way as to produce a symmetry or 
pattern, the term merism is applied. . 
Symmetry may affect the proportions and shape 
of the body of an animal or plant as a whole, or, on 
the other hand, separate parts or organs may show a 
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