116 EVOLUTION 



the darkness of the past; and it is only 

 when we know securely what changes are 

 going on now that we can legitimately argue 

 back to what may have occurred in remote 

 antiquity. 



Facts bearing upon variations have been 

 gathered so industriously of late that as- 

 similation has hardly kept pace with accumu- 

 lation; and one evidence of this is to be found 

 in the confusing ambiguity of the terms used 

 by various biologists. The term "varia- 

 tion" is used in reference to at least three 

 readily distinguishable kinds of organic 

 change, and the term mutation is also used 

 in three senses. The terminology will require 

 to be standardized by some International 

 Congress of Biologists; but pending this, 

 let us do what we can in trying to get the 

 ideas clear. 



When we compare a number of members of 

 the same species men, ruffs, garter-snakes, 

 sticklebacks, snails, brambles, buttercups, 

 pansies, and so on we find that they differ 

 from one another. These differences can be 

 measured and registered under the title 

 "observed differences," which commits us 

 to no theory whatever. 



But these "observed differences" require 

 further analysis before a statement of them 

 can be very useful. Indeed a statement of 



