THE GROWTH OF GROUPS 131 



if a thousandth part of the mutants which appear were 

 to form groups, the profusion of groups would be much 

 greater even than it is. 



Mr. Tower has other judgment, leading him to the 

 opposite conclusion. He has placed on record some most 

 valuable facts, and has summed them up according to it. 

 Let us bring both judgments to bear on the same facts in 

 succession. In order to make such a comparison it is 

 necessary to quote again from the memoir. The argu- 

 ment against the efficacy of mutants, opens as usual with 

 the declaration that they are too few in number to be 

 able to make any headway against the preponderating 

 normal multitude. The question of numbers is important 

 and as a result of much labour Tower has shown exactly 

 how rare (or how common if we choose to express it so) 

 mutants are among the potato beetles. He then states 

 his belief that they are too rare to be effectual, in the 

 following words : 



" From these records in nature we see the great rarity 

 of these forms, and taking all the counts, out of 207,891 

 beetles examined there were 118 sports, or in the ratio 

 of 1761 to i. This high ratio, however, is due to the lot 

 from Cabin John Bridge, where there were an enormous 

 number of sports, due to most unusual conditions of 

 environment." (The number was 82 sports of four kinds 

 among 11,792 beetles collected in one field.) " If we 

 remove these the remaining 196,099 show 36, or in the 

 ratio of 5447 to i. Taking all the available data gathered 

 from 1894 to 1904, I find that on the average about one 

 beetle in six thousand is of the class which is designated 

 as sports, discontinuous variations, or mutants." A com- 

 mentator with other judgment might object to the Cabin 



