220 Dr. Mac Culloch on the changing 



seem to be especially provided with the means arid the desire or 

 feeding on shell-fish ; others on crabs or the crustaceous insects ; 

 while the northern whale, by an arrangement which most 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 witii respect 

 to many fishes, we should be tempted to 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, have 

 long 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 sufti- 



