130 THE THEORY OF MUTATION 
separate symmetry of their own. For the phenomena 
thus distinguishable separate terms are proposed. A 
major symmetry is a form of pattern which includes the 
body as a whole, as in the case of most animals where 
the two sides of the body closely resemble one another. 
A minor symmetry is a pattern completed in a separate 
organ or part—for instance, in the flower of a plant or 
the limb of an animal. 
Once more we may lay stress upon the universal 
existence of pattern among living things. Bateson 
points out that in collecting any kind of living creature 
it is the symmetry of it which, as a general rule, first 
catches the eye and distinguishes the organized body 
from surrounding inanimate objects. 
The phenomenon of merism or repetition of parts 
being understood, we are in a position to consider the 
subdivision of variations into meristic variations and 
substantive variations respectively. 
Meristic variations are variations in symmetry and 
in the number of repeated parts. A change in the 
number of organs in a series may conceivably take 
place gradually by the addition or subtraction of suc- 
cessive fractions of a part. But, as a matter of fact, 
this is very seldom the case. The increase or decrease 
usually involves one whole member at a time and some- 
times more, so that this kind of variation is, as a rule, 
discontinuous. Abundant illustrations of this fact are 
to be found in the case of changes in the number of 
such parts as the teeth or vertebre of mammals ; and 
a particularly good instance is afforded by the variations 
which take place in the number of ray florets in various 
