NERVOUS SYSTEM, SENSES, AND SENSE ORGANS 191 



and inner ear. In the fish the first two of these are entirely 

 wanting, there being no outer meatus or trumpet, no ear-drum, 

 and no Eustachian tube connecting the middle ear with the 

 pharynx, and the inner ear itself is of much simpler design. 

 The membranous sac is partially constricted into two portions, 

 an upper chamber or utriculus, and a lower or sacculus: a 

 small sac-like outgrowth from the latter, known as the lagena, is 

 all that is developed of the spirally twisted cochlea, the essential 



anterior canal 



•duct for c'ulolum.ph. 



^^ utriculus 

 •po<$terior caned 



---- horizontal canal 



iaoenu 



a 



Fig- 75- — AUDITORY ORGAN OF A TYPICAL FISH. 



a. Otolith (Sagitta) of Cod {Gadus callarias), X f ; b. The same of Meagre 



{Sciaena aquila), X f . 



seat of hearing in the higher vertebrates (Fig. 75). Connected 

 with the utriculus are the three semicircular canals, which play 

 an important part in the maintenance of balance, two running 

 in a vertical direction and placed at right angles to one another, 

 the third horizontal. At one end of each of these canals is a 

 swelling, the ampulla. In the Lamprey [Petromyzon) the 

 horizontal canal is wanting, in the Hag-fish {Myxine) there is a 

 single canal with an ampulla at each end, but in other fishes 

 all three canals are developed. 



In the embryo fish the auditory organ originates as a hollow 



