GENERAL FACTS ABOUT SEA FISH 29 



if not indeed a volume, to itself. A brief summary of the 

 first principles is all that can here be attempted. 



The student of the distribution of land animals, beasts, 

 birds, reptiles, or fresh-water fishes, has at once a simpler and 

 more complex task before him than if his theme were the 

 fishes of the sea. In the first place, the subject has been fuUy 

 worked by many naturalists, and the zoo-geographical zones 

 are, with some little modification here and there, satisfactory 

 for all such purposes. If we take the case of a land mammal, 

 like, for instance, the camel, we know, with a little research, 

 that, apart from the teachings of palaeontology and the 

 artificial transplanting by man (as in South Australia and 

 Italy), the camel is an Asiatic animal which the Arab has taken 

 into Northern Africa. We know also that the New World 

 has not, at any rate to-day, any animal of the same species ; 

 but we find in the llama, vicuna, and huanaco of the Andes 

 region what are known as " vicarious " species — that is to 

 say, closely allied animals, sprung from a common ancestor — 

 which may be said to replace the camel on that side of the 

 Atlantic. In the case of most mammals, at any rate, save 

 perhaps flying bats and swimming porpoises, a mountain range 

 or a deep sea will form a sufficient hindrance to progress, and 

 in this way the fauna of some islands has, from long isolation 

 since the older land barriers were swamped beneath deep 

 waters, arrived at a remarkable stage of types peculiar to very 

 small areas of the world's surface — that is to say, found 

 nowhere else at the present day. 



With the fishes of lakes, which are, so to speak, the 

 converse of islands, there may be a similar isolation, and we 

 know, in fact, that the chars of some countries, possibly even 

 of our own Welsh lakes, differ in their characters from those 

 of other parts of the world. 



In the case of sea fish there is obviously no such straight- 

 forward course of study. Indeed, when we consider how 

 apparently easy it is for a fish to swim on and on without 



