1 84 SCIENCE SKETCHES. 



are unintelligible. If the variation of species is 

 really immutability in disguise, we cannot trust 

 our senses. It is said — I know not on what 

 authority — that the distinguished ichthyologist 

 Albert Giinther was converted to Darwinism by a 

 study of the British salmon. Whether this is true 

 or not, such a study could have no other effect. 

 If a personal reference be permitted, I may say 

 that I was brought to my present beliefs by a 

 study of the minnows and darters of the Missis- 

 sippi Valley. In the study of species one has 

 no choice except that between some form of a 

 development theory and a hopeless, unscientific 

 agnosticism ; and in all forms of biological inves- 

 tigation — the study of Comparative Anatomy, 

 Morphology, Embryology — similar results are 

 invariably reached. 



I have purposely avoided the use of the word 

 " evolution " in connection with Darwin's work. 

 ** Evolution " is a term belonging to metaphysics 

 rather than to biology. The theory of evolution 

 is that there is in all things a tendency to become 

 specialized and differentiated, — that, in accord- 

 ance with this tendency, nebulous masses have 

 become concentrated into planets, and that all 

 forms of life have changed from the simple to the 

 complex, from the low to the high, from homoge- 

 neity to variety. From the study of the history of 

 the globe and its life we find that many changes 

 such as this theory contemplates have indeed taken 

 place ; that progress has been the rule and retro- 

 gression the exception. Degraded forms exist in 

 all groups, as degraded races among men; but 



