BRITISH FRESH-WATER FISHES 
Tae 
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, 
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