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ON THE LOCATION OF THE SACCULUS AND ITS 

 CONTAINED OTOLITHS IN FISHES. 



By Colonel C. E. Shepherd (Indian Army). 



Whilst as a rule every fish that has otoliths has six of them 

 (three each side), in different families they are located in the 

 head in different ways, and these are characteristic of the 

 families. The otolith in the sacculus is the sagitta, the otolith 

 in that portion of the sacculus known as the lagena is the 

 astericus. In many fishes the position of the sagitta, the bone 

 of the skull being very thin immediately under it, becomes 

 apparent on removing the epibranchial arches and the adjacent 

 tissues, the opaque body of this otolith showing distinctly 

 through the thin bone. This, however, is mostly seen in the 

 case of a fresh head ; those that have been preserved in any way 

 often lose this transparency of the bone, although in some 

 cases it is retained. This transparency is not peculiar to any 

 fish in particular, but is to be seen in many different families, 

 whilst other members of the same family do not show it. It is 

 to be observed in Gadus merlangus (the Whiting) ; in several of 

 the Pleuronecticlce (the Flat fishes) ; in several of the Characinidcs, 

 and many others which will be mentioned later on. In the 

 cases where the sagittse can be seen they are always inclined at 

 an angle to the middle line down the length of the fish, the 

 backward end of the otolith being nearer to the middle line and 

 the end pointing forward being' further away, so that a line 

 drawn through the direction. of the otoliths would make an acute 

 angle with the middle line, the apex of the angle being directed 

 backward. When the thickness or opacity of the basi-occiput 

 does not permit of the sagittse being seen, their position is often 

 indicated by a more or less defined, prominent bulging of the 

 bone on each side of the middle line. In some fishes the 

 position of the sagittse is shown by two bony excrescences on 

 the under side of the skull, diverging from one another to suit 



