12 



THE SEA-TROUT 



picture which we form of it, one may now inquire how far the student 

 of natural history has helped to bring the picture into proper focus. 



Here again, at the very beginning, one who, like myself, is 

 accustomed to the practical rather than the scientific aspect of fish life, 

 will encounter a difficulty, and perhaps I can best explain it by quoting 

 from a letter on the subject which I have received from one of the 

 students aforesaid. 



" If you look," writes my friend, " at the Article ' Ichthyology ' in 

 the ' Encyclopaedia Britannica ' (last edition), you will see that it is 

 divided into two sections, one on the morphology of fishes and one on 

 the classification of fishes. Now this division is a simple expression 

 of the fact that the whole subject is so divided and that the workers 

 upon it are similarly divided. The two types of workers occupy 

 somewhat different standpoints towards such conceptions as variety, 

 species, family, and so on. The morphologist looks on them as merely 

 convenient groups into which to arrange animals, expressive of their 

 blood-relationship in an evolutionary sense. He is interested in the 

 features of the various groups in so far as they are evidences of this 

 blood-relationship. He does not admit that there exists in nature any 

 general grouping of animals agreeing with what we call genera, families, 

 and so on. He says that you can only form a conception of ' genus,' 

 or ' family,' or ' order,' if you restrict your view to one isolated group of 

 animals. Thus within the group ' Birds,' you may have a fairly clear 

 idea of what you mean by each of these terms; similarly within the 

 group ' Dipterous Flies,' or within any other group. But he does not 

 see any evidence that ' family,' or ' genus,' means the same thing in 

 these different groups. In each case it is .simply a convenience evolved 

 by specialised systematists within the particular group. The sys- 

 tematist, on the other hand, tends to look on such groups as represent- 

 ing, so to speak, well-defined conceptions in nature. His interest is in 

 cataloguing animals and separating them into the various groups. He 



