LOCATION OF THE SACCULUS IN FISHES. 



107 



MoEMYEIDiE. 



In this family the sacculus is at the back of the skull, to one 

 side, away from the middle line and separated from the cavity 

 holding the brain by a diaphragm of a thick skin-like substance. 

 The ear membranes are attached to an ovoid-shaped bladder, a 

 prolongation of the swim-bladder. The whole arrangement is 

 totally different from that of any other family of fishes. This is 



Artt 



Post/ 



Fig. I. 



1. Neoceratodus fosteri. 2. Hyodon alosoides. 3. Osphromenus OLFAX. 



4. Otoliths from right side only of Polynemus tetradactylus. 



seen in Mormyrus kannume, Hyperopisus bebe, and Marcusenius 

 isidori, all from the Nile Eiver. In Mormyrus kannume the 

 lapillus is the largest otolith of the three (fig. II., 11, p. 109). It 

 is, however, nearly equalled by the astericus. The length and 

 breadth of the two are nearly equal, but in thickness the lapillus 

 is the greater, the astericus being, as is usual with this stone, 

 comparatively thin. 



Hyodontidje. 



Hyodon alosoides (the Mooneyes of Canada) has no outside 

 evidence of the position of the sacculus as far as the bones of the 

 skull are concerned; but it may be noted that the sacculus lies 



