NERVOUS SYSTEM, SENSES, AND SENSE ORGANS 193 



capsule enclosing the auditory organ, and this is closed by a 

 fine membrane. A tube-like outgrowth from the front end of 

 the air-bladder comes into contact with this membrane on 

 the outer side. In some of the Herrings {Clupeidae), and in the 

 Mormyrids (Mormyridae), the apertures in the capsule are open, 

 and processes from the air-bladder actually come into contact 

 with protruding outgrowths from the utriculus itself. In the 

 Characins, Gymnotids, Cyprinids {Cyprinoidea) ^ and in all Gat- 

 fishes {Sihiroidea), the connection between the air-bladder and ear 

 is much more elaborate, and these fishes are grouped together 

 under the name of Ostariophysi, derived from two Greek words 

 meaning "a small bone" and "inflated." The connecting 

 apparatus, known as the Weberian mechanism (after its dis- 

 coverer, Professor Weber) , is formed by the modification of the 



I-' y 



..~Air-bUcUer 



Fig. 76. 



Section of the skull of Carp {Cyprinus carpio), showing the Weberian mechanism, 

 X i. I-IV. Weberian ossicles. 



first four vertebrae immediately behind the skull, certain parts 

 of which have become separated off and form a chain of Httle 

 bones or ossicles on each side, linking up the air-bladder with 

 the perilymph-filled spaces surrounding the inner ear. The 

 names of these ossicles need not be given here, but it may be 

 pointed out that the first two represent the much modified 

 neural arch of the first vertebra, another is a portion of the 

 second vertebra, and the last represents the modified rib of the 

 third vertebra (Fig. 76) . 



The exact function of this remarkable mechanism is not yet 

 fully understood, and it may be connected with the perception 

 of movements in the water, or alterations in pressure, or perhaps 

 serves to accentuate the sound waves and thus act as an 

 accessory organ of hearing. Since the mechanism occurs almost 

 entirely in fresh-water fishes, living in water where the range 



