BRITISH FRESH-WATER FISHES 



The illustrations accompanying the history of the 

 Trout (Figs. 33 to 36) will convey a better impression 

 than any written description of the life-cycle of a fish, 

 and it may be taken as a typical example of many, if not 

 most, of them. Reference should be made to the above 

 illustrations, and also to the notes upon the Trout on 

 page 67. 



Fishes obtain oxygen from the air dissolved in the 

 water, by means of internal gills, but it should be pointed 

 out that all creatures that live in water, although verte- 

 brates, like fishes, do not belong to the finny tribe. 

 The Whale and Seal need only be mentioned as examples 

 of these, both, of course, being mammals and not fishes. 



For lessons on the geographical distribution of fishes 



the reader must be referred to a larger treatise than this 



popular little volume pretends to be, but a few words 



must be written, by way of concluding this introduction, 



as to what constitutes a fresh- water species. It does not 



follow that because the familiar Stickleback is found in 



a wayside streamlet, so tiny that one can leap across it, 



that it does not also inhabit the sea. The reverse is 



also true, namely, it does not follow that because the 



Shark is found in the sea that it also occurs in fresh 



water. The fact is some kinds of fishes are equally 



well at home in fresh or salt water, and the same species 



is also found occupying both territories. Then again 



there are exclusive fresh- water dwellers, as there are 



exclusive sea-water dwellers, and there are again others, 



like the Salmon, which spawns in fresh water, and others, 

 58 



