134 Dr. Hancock on the Mullets of Guianat 



electricus), as also in the cod. It burns with a brilliant flame, 

 giving out the smell of gunpowder in its combustion. The 

 varieties exhibited in the form and structure of this organ, in 

 different fishes, are very curious. In many, it is an extremely 

 thin, light, and pellucid membrane, or bladder ^ properly so 

 termed ; in others, it is thick and spongy, or of a cellular 

 structure. In the gilbagre, it seems as it were a solid mass of 

 glue, weighing at least a pound in a full-grown fish *. At the 

 same time, it may be much inflated by blowing with a quill, 

 inserted into the anterior part, where it appears to be connected 

 with the gullet, and the gill apparatus. 



In some fishes the bladder is not obvious, until inflated, 

 and this I have recently found to be the case with respect to 

 the cottus scorpius : — On opening this fish, I observed, as I 

 thought, an ovarium, which was attached by a membrane along 

 the spine, and by some cords to the anterior dorsal vertebrae. 

 Having observed this to be the usual attachments of the air- 

 bladder in other fishes, although there was no appearance of a 

 bladder in the present instance, I was induced to insert a tube 

 on the side next the spine, by which means the part I had 

 taken for an ovarium, or a membrane in contact with it, was 



due position in the water ; as, in loading a vessel, no one would place the lighter 

 articles at the lower part of the hold. 



In the pleuronectes, as in all other fishes, the bladder is placed next the spine, or 

 vertebral column ; but the spine in these fishes approximates nearer the anterior 

 part of the abdomen than to the back, which brings the bladder likewise somewhat 

 forward of their centre of gravity ; and this may be the reason why these fishes 

 swim on one side and affect the bottom — at the same time their extended fins en- 

 able them to preserve their horizontal position and equipoise in the water. I may 

 further observe, that what is here stated is more to fix the attention of naturahsts 

 to these apparently neglected points, than to enunciate any opinions of my own. 



* It might afford a profitable article of trade taken to Eiurope, one sound con- 

 taining as much fine ichthyocolla as is sold in London for ten or twelve shillings j 

 and the fish may be caught in vast abundance on the coast of Guiana. 



The gilbagre is a viviparous silurus ; its colour is yellow, which can be easily 

 wiped off, as the colouring substance consists merely of a coat of slime or 

 mucus, which invests the body of the fish. A most extraordinary kind of articu- 

 lation exists in the junction of the strong spine of the anterior dorsal fin with the 

 scapular bony helmet ; forming as perfect a hinge as could be made by art — 

 and in respect to composition, the two pieces are quite entire an4 inseparable, 

 like two links of a chain. This catenated joint (unknown to anatomical science) 

 may perhaps be found in some others of the armed siluri, but I have not observed it. 



Two bones of great hardness and density lie in contact with the brain — doubt- 

 leas of the kind which are considered as the ossicula auditus, and contributing to 

 the sense of hearing ; although they are more than thrice the size of those in the 

 cod, which, M. Cuvier says, are larger than in any other fishes; each bone 

 weighing in a full grown fish about aeventy or eighty grains — ^aot twenty, as I had 

 stated by mistake in a former paper. 



