GREA T BRITAIN. 2 1 



two rounded lobes, placed side by side, beneath the bodies 

 of some of the anterior vertebrae, and where they are 

 almost entirely enclosed in bone. The pneumatic tube, 

 however, is still found to exist. Passing on to the sheat- 

 fishes, Siluridce, we find the air-bladder remarkably modi- 

 fied, in the majority of instances being apparently more 

 useful for acoustic than for hydrostatic purposes. They 

 lead the life of ground-feeders, and the power of employing 

 their air-bladder as a float appears to be subservient to 

 that of hearing. In the marine forms it has thickened 

 walls and the parapophyses of the first vertebrae (ex. Arius 

 snbrostratus] form expanded plates, to the under surface of 

 which this organ is attached. But in the more inland 

 forms the air-bladder is more or less enveloped in bone, 

 until it becomes as I have described it as existing in the 

 loaches (Nemackeilus). The chain of auditory ossicles con- 

 necting the air-bladder with the internal ear is confined, so 

 far as I am aware, to the fresh-water Cyprinidae, Chara- 

 cinidae, and to the Siluridae. 



Among the marine physostomous forms, the communi- 

 cation between the internal ear and the air-bladder exists 

 by means of caecal prolongations from the air-bladder, and 

 not by auditory ossicles. Due possibly to the absence of 

 ears, many of our fishermen have denied the sense of hear- 

 ing to fishes, which they would probably not do were they 

 aware of the existence of an internal auditory apparatus in 

 this class of animals. We find a membranous labyrinth, 

 consisting of a vestibule which dilates into one or more 

 sacculi, separated by a narrow canal from the "alvens 

 communis," and containing two or more auditory ossicles 

 or otoliths, which consist of carbonate of lime, besides 

 which it has a fluid or " endolymph." There are likewise 

 present the three semicircular canals. A true tympanum 



