lo6o FRESH-WATER BIOLOGY 



In over half of our fresh-water fishes the air bladder is connected 

 by a chain of ossicles with the ear. In some of them the air 

 bladder comes in contact with the skin in an area just behind the 

 head. The intercostal muscles are not developed at this place and 

 a form of tympanum is thus produced. It has been suggested that 

 this Weberian apparatus, as it is called, is in reality an auditory 

 organ ; that it is a static apparatus controlling the rising and sink- 

 ing of the fish in water; that it is a manometer acquainting the 

 fish with the degree of pressure that is exerted by the gases in the 

 air bladder against its walls; that it is a barometer acquainting 

 the fish with the variations in the atmospheric pressure; that it is 

 a sound producer. Judged by its structure alone, in some forms 

 the air bladder is divided into two small lateral parts connected 

 with the ossicles, the rest of the air bladder having disappeared, it 

 seems more than probable that it is an organ for the perception of 

 sound. 



Vibrations of lower frequency than those producing sound, such 

 as may be produced by waves or bodies falling into the water, are 

 perceived by the lateral line organs of fishes. The lateral line 

 organs of the head of the blindfishes are greatly exaggerated and 

 their ability to perceive vibrations enables these fishes to secure 

 living prey with precision. The lateral line organs of the head 

 take the place of the eyes of pelagic fishes in detecting food. Fer- 

 nandus Payne succeeded in getting an Amblyopsis to respond to 

 the water dripping into its aquarium. It would rise to the point 

 where the drop of water struck and would try to seize it by snap- 

 ping at it. Perception of vibrations by the lateral line organs of 

 the head enabled it to locate the point of impact of the water. 

 Touch, taste, or smell could have nothing to do with it. These 

 fishes may touch recently-crushed amphipods on which they feed 

 without paying any attention to them unless a stray leg is still 

 moving. They will readily take meat attached to a string held in 

 the hand to give it motion. 



Many fishes are conscious of the presence of food by perceiving 

 it either through the sense of smell, touch, or taste. Parker has 

 demonstrated that the catfish can detect minced earthworms by 

 its sense of smell. The elaborate experiments of Herrick with 



