FISHES. 
251 
CHAPTER XXVII. 
Pisces (Fishes). 
In passing from one country to another, we do not find 
any boundary lines in nature corresponding to those which 
we see upon our maps. There may be a gradual change 
of features, indeed ; as the vegetation that characterises 
Spain differs from that of France, and this latter from 
that of Prussia ; but the traveller is not conscious of any 
abrupt change, the last mile of his journey on one side 
of either frontier being pretty much the same as the first 
mile beyond it. We speak, too, of the various ranks and 
classes of society : the labourer, the artisan, the trades- 
man, the manufacturer, the merchant, the professional 
man, the scientific man, the statesman, the peer, the 
prince, the sovereign ; but the homes, the raiment, the 
manners of these, though characterised by well-marked 
diversities and peculiarities, are not separated by broad 
lines of demarcation, but pass imperceptibly into each 
other. The diversities exist in nature, but the boundary 
lines are arbitrary. 
So it is in Natural History. The student will do well 
to bear in mind continually that those subdivisions of 
organic beings which we call Classes, Orders, Families, 
and Genera, aro but convenient aids for recording and re- 
