VOL. XLV.] PHILOSOPHICAL TRANSACTIONS. 46/ 



may possibly be the organs more immediately sensible of the slightest motions in 

 the medium wherein they dwell. The curious, who have observed the fins of 

 fishes with the microscope, find them to be composed of infinitely fine vessels, 

 arteries, veins, muscles, and membranous fibrillae, whose structure seems more 

 delicate than is necessary for parts that serve only as oars to waft the fish along. 



At other times, if by striking on the top of the jar with a small key, the 

 stroke or tremor has been a little more violent, the fish would shut down their 

 back fins in a moment, and remain motionless at the bottom of the glass. The 

 sudden appearance of his hand at the top of the jar would likewise produce the 

 same effect; but noises made near them seemed to give them no disturbance. 



If the eyes of fishes be carefully examined, when swimming in a glass vessel, 

 the cornea or black uvea of their eyes may be seen, sometimes advancing for- 

 wards, and at other times retiring back, just as their sight is directed to near or 

 distant objects, through a grosser or finer medium ; the form of their eyes alter- 

 ing, as occasion requires, to make them distinguish objects; and their eyes have 

 so great a liberty in the orbits, that they are able to turn them any way, upwards, 

 downwards, to one side or the other, nearly a quarter of a circle, which makes 

 them fiill amends for the want of motion in their necks, and enables them to 

 change or direct their optical axis to any designed place in a moment. 



Those who have been accustomed to fly-fishing can bear witness, that the sight 

 of fishes is quick and distinct almost beyond belief: for it is not uncommon to 

 behold a fish dart itself "20 or 30 yards in an instant at a fly thrown out at the 

 end of a long line, and catch it even before it can well touch the water. Few 

 other creatures are perhaps capable to distinguish objects so small at so great a 

 distance, at least not so perfectly as these do; for, let the artificial fly differ in 

 colour, shape, or size, but very little from the natural one it should represent, 

 and not a fish will meddle with it. 



These instances of the exquisite feeling and seeing of fishes, together with 

 their want of organs that can be certainly known to serve them for hearing, as 

 well as of sufficient facts to prove that they do hear, might, he thought, amount 

 to the highest probability, that they are really destitute of that sense,* and have 

 no need of it, notwithstanding the contrary opinions of some authors: and their 

 living in an element, where land animals are capable of remaining but a very 

 short time, may render an absolute certainty in this case unattainable. 



But in order to discover what land animals can do, or what fish, had they 

 organs of hearing similar to those of land animals, would be capable of doing, 



* It is not hereby denied, that fishes of the cetaceous kind may probably hear, as well as some 

 other kinds produced in the sea, that have parts in common with land animals. These observations 

 arc confined to the coinmon fish of our rivers. — Orig. 



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