6 
INDIAN FRESH-WATER FISHES. 
the several species. In short, it is now possible, thanks 
to the painstaking labours of our predecessors, to 
attempt a popular work on this subject without in- 
curring the danger of running into serious error. 
So much for the difficulties ; but the study of 
Ichthyology has one great advantage, which is this. 
Fishes are very slightly subject to variations at dif- 
ferent ages and under different circumstances. With 
birds one species may have a plumage for winter use, 
and a different dress in summer, or the young may 
have very little resemblance to the old bird, or the 
male to the female. With insects the larval and 
pupal forms have to be studied as well as the mature 
insect, and similar uncertainty occurs in other classes 
of the animal kingdom. With fish this is rarely the 
case ; the sexes hardly ever differ in appearance, and 
the young of most species possess all the characteristics 
of the full-grown fish (there are exceptions of 
course to this as to most general rides). It is as 
easy, for instance, to identify a mahaseer of two inches 
in length, as one of four feet. 
In India the study has special advantages. Hardly 
anywhere in India are specimens not obtainable at 
any time of year, and in great variety : each tank or 
stream has an interest of its own, and if a person is 
unable to go out and collect for himself, it is always 
easy to employ fishermen, who bring specimens to the 
house where they can be examined at leisure. 
A matter of great interest connected with the 
