16 THE GROWTH OF GROUPS 



sometimes appear as characters ; for example, the whole 

 tail in mammals and birds and the horns of cattle which 

 may be congenitally absent without affecting the rest of 

 the body. 



3. There is a relation between characters and man's 

 perception of them which may be clearly recognized. 

 Some characters are easy to see, while others are more 

 difficult. We are apt to regard this relation as though 

 it were quantitative, but it is not so in reality. A 

 character that can only be seen with the help of the micro- 

 scope may seem to be smaller than one visible to the 

 naked eye, but quantitatively it is not so ; for if we 

 measure characters by their degree of visibility, where 

 in the scale shall we place characters such as immunity 

 from a particular disease, or where shall we place a 

 character which is appreciable as an instinct or kind of 

 activity. To regard this relation between various cha- 

 racters as quantitative is confusing, since there seems to be 

 a real quantitative relation between characters which is a 

 different matter. 



How shall we express this peculiar relation ? To 

 call them major and minor is objectionable, since one is 

 not larger than another. We should not speak of them 

 as important and trivial, since an invisible but otherwise 

 appreciable character may be of the utmost importance. 

 The taxonomist usually regards them in this manner and 

 overlooks those which are trivial. We must not speak 

 of them as clear and obscure, for we can only deal with 

 them when they are clear enough to be real. It is best 

 to think of them as obtrusive and unobtrusive. We 

 may say that various characters obtrude themselves upon 

 our notice differently, and we must remember that their 



