i6o OUTLINES OF ICHTHYOLOGY. 



the carnivorous species as to have been compared 

 to the action of fire and water combined. 



The process is most rapid, and the intestines 

 shortest, in those species which live principally, or 

 wholly, on animal food ; and the intestines are con- 

 siderably longer, and the digestion proportionably 

 slower, in those which feed on vegetable sub- 

 stances. In some species, such for instance as the 

 Grey Mullet and the Gillaroo Trout, which swal- 

 low their prey whole, the walls of the stomach are 

 thickened so as to afford increased muscular 

 power, and in such species the stomach has a con- 

 siderable resemblance to the gizzard of a bird. 

 The intestines and stomach differ materially in dif- 

 ferent families. The kidneys are situated under 

 the spine. 



The Brain of fishes, which is exceedingly small, 

 is formed, as already pointed out, by an enlarge- 

 ment of the extremity of the nervous axis, or 

 spinal marrow, and is disposed as in reptiles, with 

 the addition of " nodes " or " ganglions " at the 

 base of the nerves of smell. 



The proportionate weight of brain in a Pike, as 

 compared with its body, is as i to 1,300; in the 

 Shark, as i to 2,500 ; and in the Tunny — a re- 

 markably stupid fish — but as i to 3,700. 



The Swimming- (or Air-) Bladder, is one of those 

 organs which would naturally appear to be most 



