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 vertebras of mammals ; and 

 a particularly good instance is afforded by the variations 

 which take place in the number of ray florets in various 



