LOCATION OF THE SACCULOS IN FISHES. 141 



bony pocket open at the top ; the lagena is a long protruding 

 continuation of the sacculus holding a fairly large asteriscus. 

 Seriola dummerilii (one of the " "Yellow Tails ") and Temnodon 

 saltator (the " Skipjack ") require the bony pocket to be cut away 

 to get out the sacculus. 



Scombrid^. 

 This family have small sagittse for the size of the fishes. In 

 Sarda mediterraneus * (the " Pelamid ") (Couch) the pocket for 

 the sacculus is small, it inclines upwards, and is embedded in 

 bone with a small opening at the top. It is situated well in the 

 posterior part of the skull. From Auxis rocheii,* the sacculus 

 could be extracted through the opening at the top without any 

 cutting away. In Cybium commersonii, an Indian fish, the 

 sacculus has to be cut out. In Scomber scombrus (the Mackerel) 

 there is no external indication of the position of the sacculus ; 

 although lying in a pocket, it is not much enclosed by bone ; it 

 is visible through the opening at the top. 



BRAMIDiE . 



Brama rail has a long pocket for the sacculus, allowing this 

 to be moved backwards and forwards in it. The sagitta is com- 

 paratively small, t 



Zeiid.^. 



Zeus faber (the John Dory) has its sacculus lying openly 

 on the floor of the brain cavity, it can be picked up with a forceps 

 without further trouble. The sagitta is small and most peculiarly 

 shaped (fig. II., 4). 



PLEURONECTIDiE. 



Many of this family show the sites of the sacculi very plainly 

 to the external view by a slight excrescence of the basi-occiput, 

 the thin bone allowing the sagittse to be seen. Owing to the 

 distortion of the head in this family, the sagittse seem to lie one 

 above the other instead of side by side. In Psetta maxima (the 

 Turbot) and P. laevis (the Brill) the sacculus is contained 

 in a bony pocket. The latter fish and Pleuronectes limanda 

 (the Dab) show the site of the sacculus through thin bone. 

 P. platessa (the Plaice) shows the rings of growth of the 

 sagitta from which the age of the fish is deduced most clearly 

 when it is first taken out of a fresh head. 



* See ' Zoologist,' 1910, p. 293, pi. I., 1 and 2. f Ibid., pi. I., 8. 



