4 BRITISH FRESH-WATER FISHES 
of being world-wide, must of necessity become national— 
provincial—parochial—in its scope, as in the days succeeding 
Aristotle. 
Further: no satisfactory understanding of the fauna, or 
any class in the fauna, of any country can be had unless it is 
viewed in relation to that of the rest of the world. This is of 
special importance in dealing with fresh-water fishes, because, 
severely circumscribed by the limits of the medium in which 
they exist, the question constantly arises, How did such-and- 
such a species get into certain rivers and not into others? For 
example, the significance of the presence of the burbot in rivers 
running eastward in England, its absence from those running 
westward, cannot be appreciated unless the affinities of that 
fish are understood. When it is explained that the burbot is 
the only member of the great Cod Family known to inhabit 
fresh water, that it abounds in the rivers of Central and 
Northern Europe, as well as those of North America, a good 
deal of light is thrown upon the former connection of the 
streams of Eastern England with the great watershed of 
the Rhine. Here, again, is the need for scientific as well 
as for popular names. The burbot is a cod, but the great 
Murray cod of Southern Australia is not a cod at all, 
but a perch. 
I hope enough has been said to show that it is from no 
delight in polysyllables that I have given the scientific names 
in a work that lays no claim to contribute to the advance of 
science. The utmost that I have attempted is to describe the 
appearance, habits, and distribution of the various species, 
partly from my own observation and, in a far greater degree, 
from the records of trustworthy observers ; and at the same 
time to give an accurate impression of the position of each 
genus in the great class of Fishes. In order to do so I 
have followed generally the classification of Dr. A. Ginther, 
departing from it only in the case of the Sa/monidz, wherein 
close observation has inclined me to believe that too much 
