THE AQUATIC VERTEBRATES 1059 



only about one-third the former, while in groups three and four, 

 on the other hand, vegetation amounts to about one-third the 

 animal food. The groups last mentioned, distinguished from each 

 other as they are only by the presence of a masticatory surface 

 on the pharyngeal teeth in the first, and its absence in the second, 

 differ scarcely at all in their general food characters, and this 

 structural feature seems therefore to be of little significance. In 

 both the animal ratio amounts to seventy-five per cent, and vege- 

 tation stands in each at twenty-five; while insects are respectively 

 fifty and sixty-one." 



Recently Piitter has maintained that fishes absorb food in solu- 

 tion in the water. He found that a goldfish lived for forty-one 

 days in tap water which contained no organized food and the 

 oxygen consumed substantially accounted for the loss in weight. 

 When organic substances were dissolved in the tap water, the goldfish 

 survived for seventy-eight days, and the oxygen consumed greatly 

 exceeded the amount that would account for the loss in weight. 



Food according to its nature may be detected by sight, perception 

 of vibrations, touch, smell, or taste. 



Food is detected by sight in most fishes. Many fishes will 

 seize an object that is in motion without discrimination as to 

 what it is provided it is the right size. If it is suitable for food 

 that fact is discovered by touch or taste, or both, in the mouth 

 and the object is swallowed. If it is not fit for food it is rejected. 

 It is evident that in such cases sight only locates the moving 

 object, other senses distinguish its nature. 



Neither friend nor foe of the fishes discloses his presence by 

 sound, but frequently does so by vibrations of lower frequency. 

 It is extremely doubtful whether any sound produced over water 

 is heard by fishes in the water. The sounds of the air are scarcely 

 capable of passing the surface of the water to an extent to be per- 

 ceived by an ear imder water as highly developed as that of man. 

 The ears of fishes are much more simple than those of man. The 

 abihty on the .part of fishes to hear at all has been disputed, but 

 Parker ^ has recently made experiments that show conclusively 

 that fishes hear sounds produced under water. 



> Bull. tr. S. Fish Com., 22 : 45-64, 



