50 OCEAN LIFE. 



the various scented oils with which some anglers impregnate 

 their baits. 



"The form of the teeth in fishes is various; in general it re- 

 presents that of an elongated cone, slightly curved inwards to 

 assist in holding .a prey which is frequently alive. Sometimes 

 the form is that of a short and rounded tubercle, adapted for 

 crushing ; in some fishes the teeth are so small and numerous, 

 as to have the appearance of the hairs of a brush ; while in 

 others they are thin and flat like the incisor teeth in the human 

 subject. Some fishes that are without teeth in the mouth, have 

 them in the throat, this is particularly the case in the Carp, and 

 the allied species of the family of the Cyprinidce generally. 

 Fishes have cold blood ; that is to say, the blood does not, in 

 general, rise appreciably above the temperature of the element 

 in which they swim. It is invariably red. The heart consists 

 of one auricle and one ventricle, which receives the blood from 

 the veins, and sends it to the gills for renewal by the absorption 

 of oxygen ; whence it is circulated through the body in arteries. 

 Both the arteries and veins are perfectly closed vessels. In many 

 fishes there is a large bladder situated within the body between 

 the spine and the bowels ; it assumes various forms, and is always 

 filled with air, which, in marine fishes, is principally composed 

 of oxygen. It is supposed to be connected with the buoyancy of 

 the animal, and hence is often called the swimming bladder ; 

 but there are structural reasons for considering it to be the first 

 rudimentary form of an air-breathing lung. 



" The air bladder does not occur in all fishes; some fishes, and 

 those particularly that live near the bottom of the water are 

 without any. ' The swimming bladder of fishes/ says Dr. Koget 

 in his excellent Bridgewater Treatise, ' is regarded by many 

 of the German naturalists as having some relations with the re- 

 spiratory function, and as being the rudiment of the pulmonary 

 cavity of land animals ; the passage of connection with the oeso- 

 phagus being conceived to represent the trachea.' Hervey long 

 ago observed 'that the air in birds passed into cells beyond the 

 substance of the lungs ; thus showing a resemblance to the 

 cellular lungs in reptiles, and the air-bladder in fishes.' M. 

 Agassiz, in dissecting a species of Lepisosteus, a fresh water 



