LOCATION OF THE SACCULUS IN FISHES. 137 



flexible bone, which allows the stones to be distinctly visible 

 from the outside. Inside, the pockets are open at the top. In 

 Perca fluviatilis (the Perch) the site of the otoliths is very 

 apparent : two bulbous swellings, one each side of the basi- 

 occiput, mark it unmistakably. The sagitta, large for the size 

 of the fish, is well embedded in a bony pocket and the lagena 

 well defined. 



Serbanid.e. 



Serranus gigas (the " Dusky Perch ") (Couch) has its sacculus 

 in a long deep pocket, with room enough in it to allow the sagitta 

 to be freely moved backwards and forwards in it. In S. cabrilla 

 (the Comber) and S. scriba, a Mediterranean fish, smaller 

 members of the family, the sacculus is more boxed in; the sagitta 

 has not so much room for motion. In Apogon rex mullorum the 

 thin bone below the sacculi permits the sagittas to be clearly 

 located; they are large for the size of the fish. Ambassis 

 urotcenia has two large, almost hemispherical, protuberances of 

 thin bone under the sacculi ; the opaque bodies of the sagitta 

 show through. These stones are large for the size of the fish. 



PSEUDOCHROMIDID^. 



In Lopholatilus chamceleonticeps (the " Tile Fish " of the North 

 Atlantic Ocean) the sacculus is held in a bony pocket open at the 

 top, through which the sacculus could be seen projecting, but 

 bone had to be cut away to extract the otoliths.* 



Sclsenim;. 

 Amongst these fishes the sagitta is large, and consequently 

 a palpable swelling of the basi-occiput shows the position of 

 the sacculi and their enclosed stones. Umbrina cirrhosa (the 

 Umbrina) (Couch) has a large pocket for the sacculus well open 

 at the top, the whole of the ear labyrinth on each side was picked 

 out at once, no cutting away of bone being found necessary, the 

 semicircular canals only needed to be cut across. In Corvina 

 nigra, a Mediterranean fish, the sacculus is in a big roomy pocket 

 open along the top but closed at the ends. The lagena stretches 

 well away at its extremity of the sacculus, and has 1 a roomy 

 pocket to itself. In Nebris microps (the "Butterfish " of Deme- 



* For illustration, see 'Zoologist,' 1910, p. 294, pi. ii., 1. 

 Zool. 4th ser, vol. XVIII., April, 1914. m 



