and the Anatomy of Fishes^ 291 



other fishes, naturally double, probably diverge, from some 

 casual defect of the cohesive substance and investing mem- 

 brane. 



It is probable that the rays in these bifid portions will be 

 found to be single ; this, however, I offer only as a conjecture, 

 never having examined one of them *. 



This composition, or double structure of the fins of fishes, is 

 peculiarly obvious in the tail fin ; when denuded of its mem- 

 ^)ranes, these bones will be seen separated some distance at the 

 base ; as I have lately observed in the tail-fin of a cyprinus, the 

 skeleton of which I had suspended to dry two months since, and 

 from which the soft parts were found to have been entirely 

 removed by flies, or other insects. This specimen exhibits the 

 rays of the tail-fin, spread on each side of the expanded fan- 

 shaped bones which terminate the last piece of the vertebral 

 column ; and thus displays, without being boiled or dissected, 

 most clearly, the twin or double layers of the rays. 



It also exemphfies the great power of the tail, or caudal fin, 

 in propelling the fish with rapidity through the watery element ; 

 for each of these bones we find to have strong muscular attach- 

 ments laterally, enabling it to ply like an oar in the water, and 

 giving that powerful elasticity and flexion from side to side. 



I have been, it may be thought, rather tedious and minute on 

 this subject ; but, from the vast accession of new species which 

 have been derived from the discoveries of later naturalists and 

 travellers, it has been found in many cases, especially in respect 

 to fishes, that the characters usually employed for discrimina- 

 ting the species have become extremely defective. It is this 

 deficiency in the external characters which has induced some 

 of the most able naturalists of modern times to direct their 

 attention to comparative anatomy, for more certain means of 

 discrimination, as well as for the elucidation of the general 

 structure and functions of animals. 



I need say no more, however, on this subject, but refer to an 

 examination of the structure of the fins of fishes, in proof of the 

 facts here stated. 



* Another singularity observable in this fish, is, in numerous instances, a priva- 

 tion of tho posterior part of the dorsal fin : it is never observed to sleep ; and Mr. 

 Butler, of Covent Garden, asserts, that they thrive best without being fed. Many 

 plants flourish in water — some in air alone : it is rare, however, to mid an animal 

 Nourished without something more substantial. 



