12 Dr. Knox on the Theory of a Sixth Sense in Fishes, 



Art. III. — On the Theory of the Existence of a Sixth Sense 

 in Fishes ; supposed to reside in certain peculiar Tubular 

 Organs, found immediately under the Integuments of the 

 Head in Sharks and Rays. By Robert Knox, M. D. 

 F.R.S.E. &c. Communicated by the Author. 



In dissecting the shark, tope fish or skate, none, I think, 

 not even the most careless observer, could have missed noti- 

 cing certain groups of very singular organs, which seem as 

 it were peculiar to these families of animals. They were 

 long confounded in anatomical descriptions with the lacunar 

 or mucous system, which I believe to be common to all, or 

 at least to most fishes, until clearly shown by Mr. Jacobson 

 of Berlin, to be perfectly distinct from the latter, and differ- 

 ing probably as much in function as in structure. Mr. 

 Jacobson concluded from his dissections, that they were or- 

 gans of touch ; and however improbable this opinion may at 

 first sight appear, it seems not unlikely that it will ultimately 

 be very generally adopted. 



The organs I allude to have been long known to compa- 

 rative anatomists, nor indeed is it possible to examine even 

 with ordinary attention the head of the shark, without per- 

 ceiving very readily their general structure: — A vast as- 

 semblage of parallel transparent tubes, filled with a gelatinous 

 fluid, and supplied with large branches of nerves, communi- 

 cating with a flat surface, and as it were perforating the in- 

 teguments. Such are the organs I now speak of, and which, 

 in whatever way they are viewed, merit the highest attention 

 on the part of the comparative physiologist. 



To form a sufficiently accurate idea of these organs, the 

 reader has only to imagine a congeries of comparatively small 

 tubes, springing from a common stalk like grapes from a vine 

 branch ; of a cylindrical form, and greatly resembling in shape 

 a champagne glass ; each of these is supplied with a nerve, 

 forming as it were the stalk of the glass or tube : this is filled 

 with a gelatinous body, strongly resembling the vitreous hu- 

 mour of the eye. 



It has been said by a distinguished anatomist,* " tjjat the 



* Trcviranus. 



