ass FHILOSOPHICAI. TRANSACTIONS. [aNNO 1685. 



3d of the cetaceous or whale kind : the 3d of cartilaginous fishes, which have 

 gristles instead of bones : the 4th and last of those called spinose fishes, that 

 have small sharp bones in their flesh ; after which is annexed a large appendix. 

 In the first book are considered both the internal and external parts of fishes. 

 Next to the parts of fishes, and their uses, many things are observed concern- 

 ing their hearing, their respiration, their motions, generation, food, growth, 

 age, and their division. Thus, it is noted, concerning the eyes of fishes, that 

 they are flatter or more depressed than those of quadrupeds, but the crystalline 

 humour rounder, indeed either exactly spherical, or very nearly so. They 

 want eye-lids, and it is shown that they are not necessary to them. Concern- 

 ing the hearing of fishes ; it is remarked, that in no fishes, besides the cetace- 

 ous kind, have hitherto been found any auditory passages or ear-holes, and 

 whether they hear or not, is a question not yet fully decided, notwithstanding 

 all the experiments alleged to prove the affirmative. * Concerning the gills of 

 fishes^ it is shown, that they are only as it were inverted lungs, and are of the 

 same use to fishes as lungs to quadrupeds : that the whole mass of blood in 

 every circulation passes through the gills, as in quadrupeds it does through the 

 lungs ; only it returns not again to the heart, and therefore in fishes, both the 

 vessels which carry it to the gills, and those that bring it back, are arteries. It 

 is also proved, that fishes have a kind of respiration, as well as land animals, 

 and that the use of the air is as necessary to those as to these ; so that if it be 

 inclosed, or made any ways unfit for life, they cannot live ; as is clearly evi- 

 denced by great variety of undoubted experiments. The fins serve not so much 

 for progressive motion, as for keeping the body erect, and for moving it to and 

 fro, upwards and downwards in the water : the progression is performed prin- 

 cipally by the motion of the tail, by the sudden extension whereof, after being 

 inflected, the fish shoots itself forward with great force and velocity. Vid. Phil. 

 Trans. N° 115. The swimming-bladders, found in most fishes, serve to bring 

 the body to an equilibrium with the element in which they swim ; that so they 

 may with more facility be impelled or moved any way. That this is one use of 

 it, is demonstrated from experience, for upon breaking that bladder, the fish is 

 no longer able to support itself in the water, but presently sinks down, and 

 constantly lies groveling at the bottom. From this air-bladder there is a chan- 

 nel or passage in most fishes, leading to the mouth of the stomach, but in some 



* That fishes are endowed with the sense of hearing is now no longer a matter of doubt with phy- 

 siologists. The organs of this sense have been detected by modern anatomists in various other fishes 

 besides those which belong to the cetaceous order; as may be seen by referring to Mr. John Hunter's 

 observations, inserted in the 7 id vol. of these Transactions, and to the works of Professors Camper 

 and Monro. 



