ADAPTATIONS 393 



special connections with the organs of hearing, so that the fish 

 seems to make use of the physical properties of gases in the 

 perception of sound as well as in its production. In this respect 

 the fish, though living in a liquid, has greater resemblance to 

 terrestrial animals than we might expect, for in ourselves and 

 other vertebrates which live in a gaseous medium the tympanum 

 or middle ear is an air-chamber which is accessory to the organ 

 of hearing, and the voice is produced by the movement of air 

 from the lungs. 



There are three different modes in which the air-bladder is 

 connected with the auditory organ. In many marine fishes the 

 bony capsule surrounding the auditory organ on each side has 

 an aperture closed by a membrane, and a tubular outgrowth 

 from the air-bladder comes into contact with this membrane on 

 the outer side, while on its inner side is the liquid surrounding 

 the membranous labyrinth of the ear, the liquid called the 

 perilymph. This arrangement occurs in certain species of the 

 Gadidoe or cod family, and in the Serranidae, Berycidse, 

 Sparidae or sea-bream family, and the Notopteridae. All these 

 families belong to the spiny-finned fishes or Acanthopterygii, 

 except the last, which is Malacopterygian, or soft-finned. In 

 the second mode the apertures in the bony capsule of the ear are 

 open, and the ends of the tubular extensions of the air-bladder 

 are in direct contact with outgrowths of the membranous audi- 

 tory vesicle. This occurs in the herring and pilchard and 

 other species of the same family. In the third method the 

 air-bladder is not directly in contact with the bony capsule 

 or the auditory vesicle but is connected with the ear by a 

 series or chain of small ossicles. These bones, known from 

 their discoverer as the Weberian ossicles, are derived from the 

 first four vertebrae, of which they are separated and modified 

 portions. The ossicles are named claustrum, scaphium, inter- 

 calarium and tripus, on each side. The scaphium is inserted 

 into the wall of the auditory capsule, and the tripus into the 

 dorsal wall of the air-bladder at its anterior end. 



The possession of the latter complicated apparatus is a 

 common character of the Cyprinidae or carp family, the Siluridae, 

 the Gymnotidae, formerly known as the electric eels, and 

 certain other families, which are consequently united by Mr. 

 Boulenger in the sub-order Ostariophysi, for, as he points out, 



