126 



THE THEORY OF MUTATION 



kinds of carriages, c namely, omnibuses, hansoms, 

 and four-wheelers, are specific and excellent illustra- 

 tions of what I wish to express by mechanical types 

 as distinguished from subtypes. Attempted im- 

 provements in each of them are yearly seen, but none 

 have as yet superseded the old familiar patterns, 

 which cannot, as it thus far appears, be changed with 

 advantage, taking the circumstances of London as 

 they are. Yet there have been numerous subsidiary 

 and patented contrivances, each a distinct step in 

 the improvement of one or other of the three primary 



types, and there are or may be an indefinite number of 

 varieties in details, too unimportant to be subjects of 

 patent rights.'* 



More recently Galton might have pointed out the 

 introduction of motor traffic as illustrating a distinct 

 mutation. 



The distinction between primary and subordinate 

 positions of stability is further excellently illustrated 

 by the model which is here represented, and which 

 is known as Galton's polygon (Fig. 10). 

 * 'Natural luheritance,' p. 26. 



