LOCATION OF THE SACCULUS IN FISHES. 139 



enclosed with the sagittse but at the lower end of the sacculus. 

 In Ancylodon jaculidens (the " Weak Fish " of Demerara) the 

 decided swelling of the basi-occiput at its forward end becomes 

 almost hemispherical. The sagitta is large. In Scicena amazo- 

 nica, a South American fish, the position of the sacculus from 

 the outside is easily located. Many of the Sciaenoid fishes have 

 an excrescence on the concave side of the sagitta which is 

 notable in S. aquila (fig. III., 2). In others the excrescence is 

 formed of granules. This can be seen in fig. III., 1, 3, 4, and 5 ; 

 in No. 6 the granules are on the stone, but too faint to show in 

 the photograph. The "sulcus acousticus " in these fish also 

 takes a peculiar curved right angle bend ; this can be faintly 

 traced in fig. III., 1, 4, and 6. 



Sparine . 

 In this family the sacculus is enclosed in a bony pocket, 

 which has to be cut away to free the sagitta and asteriscus. In 

 Pagellus centrodontus (the Sea Bream) the lagena is a broad pro- 

 longation of the sacculus. In Oblata melanura, a Mediterranean 

 fish, the bone under the sagittae is thin and semi-transparent. 



MuLLnxE. 

 In Mullus surmulletus (the Surmullet) (Couch), although the 

 sacculus is in a pocket open at the top, a great deal of bone has 

 to be cut away to free it completely. 



Caproid^;. 

 Capros aper (the " Boar Fish ") has the sacculus in an open 

 recess ; the whole can be lifted out without cutting away any 

 bone. 



Ch^todontid^:. 



In Heniochus macrolepidotus, an Indian Ocean fish, the 

 sacculus is embedded in a bony pocket, which has to be exten- 

 sively cut away to release its contents. The sagitta is a fair 

 size. 



OSPHROMENIDiE. 



Osphromenus olfax (the "Gourami"), a fish from Java, has 

 the site of the sacculus marked by two prominent bulbous 

 swellings of the basi-occiput bone that project even into the 

 cavity occupied by the superbranchial organ that this fish has, it 



m 2 



