NERVOUS SYSTEM OV FISHES. 211 



braj enumerated at p. 102., as entering into tUe formationof the cham- 

 ber of the acoustic organ. In the Heri'ing a tubular prolongation of the 

 fore part of the air-bladder advances to the basi-occipital, and bifur- 

 cates ; each branch penetrates the side of the base of the skull, again 

 bifurcates, and terminates in two blind sacs, which are in contact witli 

 similar cajcal processes of the labyrinth. In the Holocentrum and 

 Sargus, CEecal processes of the swim-bladder also diverge, to attach 

 themselves to the membrane closing the part of the otocrane con- 

 taining the sac of the great otolite. 



In Osseous Fishes the sonorous vibrations of their liquid element is 

 communicated by the medium of the solid parts of their body, and in 

 some species, also, through the vibrations of the air in the air-bladder, 

 to the liquid contents of the labyrinth. In the Plagiostomous Fishes 

 the resonance in the walls of their cartilaginous cranium is less 

 than in the bony skull of ordinary fishes ; but the labyrinth is 

 wholly inclosed in the cartilage ; and a further comj)ensation is 

 made by the prolongation of its chamber to the surface of the body 

 in some, and by a similar prolongation of the membranous labyrinth 

 itself in others. The position of the external orifices on the top of 

 the head in the Skate tribe, may relate to the commonly prone position 

 of these flat fishes at the bottom of the sea. Professor Miiller con- 

 cludes, from his experiments, " that the air-bladder in fishes, in 

 addition to other uses, serves the purpose of increasing by resonance 

 the intensity of the sonorous undulations communicated from water 

 to the body of the fish."* The vibrations thus communicated to the 

 peri- and endo-lymph of the labyrinth are doubtless made to beat 

 more strongly upon the delicate extremities of the acoustic nerve, in 

 osseous fishes, by their effect upon the suspended otolites : and it will 

 be observed, that the chief portions of the nerve expand upon those 

 chambers of the vestibule, which contain the otolites. The large size 

 of the organ of hearing, and especially that of the hard otolites, also 

 relate to the medium through which the sonorous vibrations are pro- 

 pagated to the fish, and to the mode in which they are transmitted 

 to the organ ; in like manner as the eyeballs are exjianded, in order 

 to take in the utmost possible amount of light. The contracted en- 

 cephalon harmonises with and sufiices for the sensations and volitions, 

 and the simple series of ideas daily repeated in the monotonous ex- 

 istence of the scaled inhabitants of the waters. To say that the fish's 

 ears and eyes were made enormous in order to strike strongly on its dull 

 brain — that the development of the organs of sense has been exag- 

 gerated to compensate for the defective size of their nervous centres 

 — implies a want of due appreciation of the beautiful adjustment of the 



* Lxxiii. p. 1245. 



