16 Dr. Knox on the Theory of' a Sixth Sense in Fishes. 



gans so exceedingly delicate, and to advertise their possessor 

 of the presence of a living or at least a moving body. 



There is still another reason for supposing these organs to 

 exercise, though in a peculiar way, the sense of touch. It is 

 this : Linne notices several sharks as possessing a sort of cirri 

 around the mouth, and particularly under the throat and 

 lower jaw ; and the same appearances have been remarked 

 by a late observer as occurring in the enormous ray frequent- 

 ing the seas of the West Indian Islands ; now, these cirri 

 may, perhaps, be mere prolongations of the tubular organs, 

 or a substitute for them. 



• Thus it would seem that the nerves of the fifth pair under- 

 go considerable modifications in different animals, according 

 to the nature of their peripheral terminations. When ex- 

 panded in the papillae of the tongue, certain branches of this 

 nerve in most of the mammalia become gustatory ; in the 

 proboscis of the elephant, of the tapir, and in the prolonged 

 snout of the pig, mole, ornithorynchus, and duck, they are 

 true organs of touch, less perfect than the human hand 

 only by reason of the form of the organ on which the nerves 

 terminate. In certain fishes possessing labial cirri, they 

 very evidently exercise the same sensation, viz. that of 

 touch : lastly, in sharks and rays they are distributed to a 

 new organ, holding as it were an intermediate place be- 

 tween touch and hearing, but approaching nearest to the 

 latter. If we view these nerves in fishes anatomically, 

 and compare them with the true auditory, it is evident 

 that a close analogy must subsist between their respec- 

 tive functions ; for in most fishes they are so intimately 

 united at their point of communication with the brain, that 

 most comparative anatomists have viewed the auditory as a 

 branch of the fifth, (which, however, is not strictly true;) 

 whilst peripherally they each terminate in, or are expanded 

 on a substance exceedingly well adapted to perceive the un- 

 dulatory vibrations of the medium in which they live. It is 

 reasonable to think, that organs whose functions are such as 

 we have supposed these to be, would necessarily be found 

 chiefly in those animals whose habits of life most required 

 their presence ; and it would seem that in the shark they are 

 most extensively developed, and, at the same time, most ac- 

 tively employed. 



