220 Dr. Mac Culloch on the changing 
seem to be especially provided with the means and the desire of 
feeding on shell-fish ; others on crabs or the crustaceous insects ; 
while the northern whale, by an arrangement which must always 
appear extraordinary, is furnished only with the power of subsist- 
ing on animals so small as to be imperceptible, to its sense of sight 
at least, and which, in the scale of dimensions, lie almost at the 
opposite extreme to its enormous bulk. Many fish, like the cod, 
are known to be omnivorous ; and of others, it appears probable 
that they feed solely on the multitudinous tribes of vermes and in- 
sects which crowd the waters. It is probable that, with respect 
to a great number of species, they live in succession on each other, 
if that expression can be used with propriety ; or that, in the my- 
riads of animals of singular and imperfect construction, and often 
of microscopic minuteness, which crowd the ocean to a degree 
that almost surpasses credibility, provision is made for the wants, 
in succession, of all those which successively exceed each other 
in size, voracity, or activity. 
If we were to judge from what is within our reach with respect 
to many fishes, we should be tempted fo imagine that they can 
live for long periods, even without food, or with a very small pro- 
portion, Thus the cod, one of the most voracious, has been kept 
in perfect condition in Orkney, confined in sea-ponds for three 
months and more; although no visible animal was admitted with 
the water which the tide daily brought to its prison. During the 
whole residence of the salmon in fresh waters, which often extends 
to a considerable period, it seems to exist with little food ; since the 
few winged insects at which it occasionally rises, can afford no 
effectual nutrition to an animal of such bulk and activity. The 
state of the common ornamental gold-fish confined in water- 
glasses, is equally remarkable ; but it is unnecessary to prolong 
the enumeration of facts which, however difficult to explain, haye 
ong been familiar to those conversant with the habits of fishes. 
But whatever we may doubt respecting the nature or the neces- 
sary quantity of food for fishes, it must be evident that no perma- 
nent naturalization of many of them, at least, can be expected, 
unless the new situation is such as to provide them with a suffi- 
