THE CARPS 41 



Besides the lateral line organs there are diffusely scattered 

 sense organs in the skin also innervated by the lateralis system and 

 both arise from a " common rudiment in the epidermis of the embryo 

 in the position of the future auditory organ. This rudiment grows 

 baok^^•ards along the side of the body and also forwards." {Camb. 

 Nat. Hist.). This seems to be an important fact in the discussion 

 of the acoustic tubercles. There is very little known about the 

 acoustico-lateral area of fishes, except the fact that it receives all 

 the nerve fibres from the internal ear and from the several kinds of 

 lateral line organs. Herrick states " that the central terminations 

 of these different kinds of fibres are so intertwined within this area, 

 that it has not been possible hitherto to separate completely the 

 reflex centres of the many diverse functions, represented in this 

 complex system of peripheral sense organs. There is, however, 

 an incomplete separate localization within this area of several 

 specific functions, but the reflexes, served by all of the organs of 

 the acoustico-lateral comjDlex, are evidently in very close physio- 

 logical association. These reflexes fall into three groups : I. — 

 Postural and equilibrial, served chiefly by the semicircular canals of 

 the ear ; II. — Auchtory, served by the end-organs of the saccule ; 

 III. — Reactions following excitations of the lateral line organs by 

 slow water vibrations and by other agents as yet imperfectly 

 known." 



But before we enter on further discussion of the function of the 

 acoustic tubercles it will be necessary to give a short description of 

 the organ of hearing in fish, and also mention the various accessory 

 organs of hearing w^hich are found in certain families. This sub- 

 ject deserves a special chapter, as it is rather a long story, and it 

 treats of many facts which have only been firmly estabUshed by 

 recent research. 



