8 THE GROWTH OF GROUPS 



whom we may call broad-minded or old-fashioned accord- 

 ing as his methods seem to us to be good or bad. Sooner 

 or later species X will come under the notice of another 

 naturalist, who may be referred to approvingly as one 

 of the modern school or disapprovingly as a splitter of 

 hairs. He may express himself thus in regard to the 

 species X. " I have examined a large number of the 

 species X as denned by my predecessor, I can recognize 

 them plainly because they all possess the characters 

 A,B,C as defined, but I do not propose to overlook those 

 features which have been regarded hitherto as individual 

 variations ; thus, among the old species X, there are a 

 number of individuals which possess the slight but 

 perceptible character a, also there are a number of others 

 possessing characters a, b : I will therefore split up the 

 old species into three new ones x, y, z, which hence- 

 forth will be denned respectively as A, B, C, as A, B, C, a, 

 and A, B, C, a, b." This splitting process is being carried 

 on at the present day ; there is no doubt that it depends 

 on the existence of characters which, although unob- 

 trusive, can be perceived, and it seems that there is no 

 natural limit to the process. We can never be sure that 

 any particular group of vertebrate animals is indivisible. 

 Let us also consider some other opinions which may- 

 be held in regard to the splitting up of the old-fashioned 

 species. The older school of systematists who take the 

 broad view, feel that the splitting process is harmful to 

 their science, the aim of which is to trace the distribution 

 of species. They have confidence in their belief that 

 old-fashioned species such as X, which were defined in 

 terms of many clear characters, arose in one place and 

 spread from that place ; but they have no confidence 



