158 CAUSES OF VARIATION 







Meristic variation in general due to cell division. All differen- 

 tiation involving numbers of duplicate parts manifestly has its 

 seat in cell division. An additional division at the point of origin 

 of the series doubles the number, but an extra division at the 

 point of origin of a member adds a pair, if both daughter cells 

 develop, or a single member if but one develops. 



When the number in a meristic series is even the series is 

 easily conceivable as having arisen from a corresponding number 

 of cell divisions. For example : 



2 in the series, i division 



4 in the series, 2 divisions 



6 in the series, 2 divisions, with one pair dividing again 



8 in the series, 3 divisions 



10 in the series, 3 divisions, with one pair dividing again 



If the number of members is odd, it is only necessary to assume 

 that one of the even numbers failed to develop, or, what is more 

 likely, that one of a pair indulges in additional division, its 

 sister member remaining single ; thus : 



3 members, i division, one member dividing again 



5 members, 2 divisions, one member dividing again 



7 members, 2 divisions, three members dividing again 



9 members, 3 divisions, one member dividing again 



The frequent recurrence of five as a digital number is one of 

 the mysteries in creation, and its singular persistence is another. 

 It is, however, subject to many deviations, as was seen in the 

 chapter on " Meristic Variation"; even in the rose family there 

 is an occasional loss of one of the members. 



The frequent presence of six digits is not to be explained by 

 reversion, as nobody supposes that number ever to have been 

 characteristic in any species, a fact that should be noted by 

 some of our friends who are always ready to invoke the aid of 

 atavism to explain every abnormality. 



Meristic variation, like other deviations arising from external 

 causes, is to some extent hereditary, and capable of being in- 

 fluenced, if not absolutely controlled, through selection. No 

 other method is known, aside from the fact that external injury 



