ON DISTRIBUTION. 
21 
The range of species is much mere closely restricted 
than that of genera. As before remarked, very few 
species that occur in India are to be found elsewhere, 
though most of the Indian species are met with all 
oyer the Indian continent. There are a few local 
species ; some that are found only in Assam, some 
only in the Himalayan streams, some only in the 
streams of the Heilgherry hills in Madras, and so on, 
but these are generally species that live in rapid hill 
streams ; those that inhabit still water, tanks, and 
the larger rivers of the plains are to be met with all 
over India. 
A number of interesting questions suggest them- 
selves in connection with this subject. How can a 
fish, take, for instance, Kasbora daniconius, have spread 
from India to the islands of the Eastern Archipelago, 
or vice versa ? Does this point to a time when these 
islands were connected with the main land ? If 
this question is to be answered in the affirmative, we 
have here data for inferring the comparative antiquity 
of this species, as it is evident that it must have ex- 
isted before the separation of these islands from the 
main land took place, and cannot have undergone any 
perceptible variation since that time. 
Again, take a genus, Labeo, for instance, of which 
some species are confined to India, while others closely 
allied are found in Africa. This is essentially a tro- 
pical genus, which fact accounts for its not spreading 
northwards into Europe, but it would seem as if the 
relative positions of land and sea must have been dif- 
