FISHES. 
121 
surprising dexterity it darts from its tubular mouth 
a single drop of water, which never fails striking 
the fly into the river, where it is immediately swal- 
lowed by the fish. The crystalline lens in fishes is 
a complete sphere, that the rays of light coming 
through the medium of water may be sufficiently 
refracted ; but as they have little if any motion 
in the eyes, they can never bring them both to 
one focus ; therefore Dr. Monro thinks it probable 
that they may be endued with a double distinct 
vision. 
The whole race of fishes seem to be impelled by 
a voracious appetite, which induces them even to 
destroy each other ; they are constantly in action 
and perpetually at war. They mutually plunder and 
devour each other, without remorse or moderation. 
Those with the most capacious mouths generally 
commit the greatest depredations among the smaller 
fish, and these in their turn fall a prey to a stronger 
adversary. So great, indeed, is the mutual de- 
struction of species among the inhabitants of the 
water, that this element in time would cease to 
be replenished, if Nature had not provided for the 
preservation of fish, by multiplying them to such 
an astonishing degree, that their fecundity exceeds 
their natural impatience to devour one another. If 
we only attentively consider the roe of a fish, we 
shall no longer wonder at the vast numbers which 
inhabit the water, notwithstanding all the casualties 
to which they are exposed. Three persons under- 
took to number the roe in a very fine cod : one of 
