14 
INDIAN FRESH-WATER FISHES. 
forms which differed from each other ages ago should 
have thrown off convergent branches, so that the 
descendants of each, becoming more and more like 
each other, should now be undistinguishable apart. 
They would still, nevertheless, be distinct species, and 
would neither consort nor breed together. However, 
though theoretically imaginable, such cases do not 
practically occur ; the developments of nature are in- 
finite, and, however closely some forms may resemble 
others, there is always some point or other, if we 
only look close enough, which serves to distinguish 
each species apart. 
A difficulty somewhat similar does, however, occur 
practically in dealing with groups. Groups perpetually 
inosculate with one another, and species may be found 
which seem in certain respects more nearly allied to 
other groups than the one to which they really belong. 
In these cases we have to discriminate between real 
and apparent affinities, and hence arise frequently 
differences of opinion between different systematists. 
The more perfect our classification becomes, and the 
closer we follow nature iu grouping such specie^ as we 
are acquainted with, by so much the less are we 
troubled with wayward forms which seem to belong 
neither to one genus or another, but to possess affinity 
with two or more. 
It must be remembered that we have at best but 
scanty material with which to build up the scheme of 
nature. We can observe the species of to-day, but 
many links are wanting, many forms must have died 
out to make room for the present ones. 
