62 BRAIN AND BODY OF FISH 



which communicates with the swim-bladder. It has an anterior 

 and posterior spherical vesicle, and we have shown that the posterior 

 vesicle has certain anatomical connections with a large lateral line 

 organ near the pterotic bone, which enables vibrations to be received 

 by the air in this vesicle, and these are conducted to the air in the 

 anterior vesicle. This vesicle is divided into two sections by a 

 transverse membrane which receives the vibrations and com- 

 municates them to the perilymph occupying the other section, from 

 whence they pass by a foramen into a space connected with the 

 saccule, and pass over a special endorgan which has a direct con- 

 nection with the medulla by a nerve ganghon. It seems probable 

 that this elaborate organ must have a special representation in the 

 medulla. It is highly improbable that the central lobe can be due 

 to any increased functional activity of the lateral line system, 

 because the herring is peculiar in that it possesses no lateral line. 

 A possible explanation of the large central area might be that it is 

 for the control of the swim-bladder, but this view is shown to be 

 untenable when we examine the functions of this organ in other 

 families as will be described later. The evidence so far seems 

 conclusive that the central area has an auditory function, and we 

 propose to call it the central acoustic lobe or area according to the 

 extent of development into a definite lobe or not. 



The hind-brain of a sprat has a similar pattern to that of the 

 herring. The central acoustic lobe appears as a large area, pear- 

 shaped in section, and fibres pass outwards to the acoustic tubercles 

 and also a definite strand of fibres leads to the lobe as described in 

 the herring. 



The examination of the hind brain of the pilchard provides a 

 sort of connecting link which binds the central acoustic lobe of a 

 Cyprinoid with the Clupeoid. It is hardly to be distinguished as 

 regards this lobe from the bleak, but the relative size is larger ; a 

 further point is the large size of the acoustic tubercles which coalesce 

 very early after their appearance with the lateral margins of the 

 granular area of the cerebellum. The special tract noted in connec- 

 tion with the central lobe in the herring and sprat is not easy to 

 distinguish. 



It will be interesting now to review aU the above facts which 

 associate the surface-feeding carps with the herring family. The 

 general appearance of the former has given rise to certain names 

 which show that early observers had been struck by the similarity 

 of certain members of the two families as regards their form ; for 

 example Engraulicypris can be translated into the English language 

 as the anchovy carp, and Isaac Walton gives as an alternative name 



