ICHTHYOLOGY. 



673 



sive motion. By means of its various flexures and ex- 



tensions, it strikes the water in different directions, but 



' all having a tendency to push the fish forward ; the ac- 

 M^Y^ 1 t ' on resembling, in its manner and effects, the well 

 known operation of the sailor termed skulling. The 

 ventral and pectoral fins assist the fish in correcting 

 the errors of its progressive motions, and in maintain- 

 ing the body steady in its position. Borclli cut off* 

 with a pair of scissars both the pectoral and ventral 

 ns of fishes, and found, in consequence, that all its 

 motions were unsteady, that it reeled from right to 

 left and up and down, in a very irregular manner. 

 The dorsal and anal fins serve to maintain the body in 

 its vertical position. But from the circumstance of 

 some of these fins being wanting, and others evidently 

 too small to produce the desired effects, those fins 

 which do exist appear to be capable of executing all 

 the movements for which the others, when present, are 

 liMgned. 



The medium in which fishes reside prevent us from 

 making any accurate observations on the velocity of 

 heir motion. Mackrel, and some other marine fishes, 

 will seize a bait moving at the rate of six or eight miles 

 an hour ; and some of the voracious sharks will keep 

 up with a vessel in her voyage across the Atlantic. 

 The darting of a salmon or trout in the water resembles 

 the rapidity of an arrow, but such motion cannot be 

 kept up for any length of time. This the angler is well 

 aware of, who, with hi* hook fixed on very slender gut, 

 will kill by fatigue the strongest salmon in the course of 

 an hour or two, and a large trout in the course of two 

 or three minutes. These facts seem to indicate, that 

 however numerous and powerful the muscles of a fish 

 may be, they are incapable of supporting a continued 



i the action of swimming, fishes are likewise 

 capable of leaping. They accomplish this by a violent 

 fort of the caudal fin, or, according to some, by bend- 

 ing the body strongly, and afterward* unbending it 

 with an elastic spring. 



A few specie* are capable of sustaining themselves 

 in the air for a short interval, and are termed Flifing- 

 Jitk. Such fish have the air bag, an organ to be noticed 

 hereafter, of uncommonly large dimension! ; hence the 

 body has great buoyancy. The pectoral fins are like- 

 wise of an extraordinary si*e. Having by a leap raised 

 themselves above the surface of the waUr, they conti- 

 nue in the air and move forward*, seldom farther than 

 a hundred yard*, by the action of tlieir pectoral fins. 

 The continuance of their flight is interrupted by the 

 drying of the membrane of these fins, when they again 

 fall into the water. 



There is one specie* of fish ( Perca scandens of Lin. 

 Trait i. vol. iii. p. 62.) which appears capable of climb- 

 ing. By this motion, according to Lieutenant Daldorff 

 of Tranquebar, it sometimes raise* itself five feet above 

 the surface of the water, mounting up the crevice* of 

 If***. The pine* of it* gill-cover retain it in its posi- 

 tion ; and when the body M bent to one side, the spine* 

 of the anal fin fix themselves in the bark ; and when 

 the body i* then brought back to its ordinary shape, 

 the bead ha* reached a higher elevation. The spines 

 of the expanded gill-covers again keep a firm hold, and 

 a similar twitting of the bodv take* place in another di- 

 rection. The spines of the dorsal fin contribute likewise 

 to this extraordinary progre*ion. The flying- fuh leave 

 the water to escape from other fishes which prey upon 

 them ; but the object to be gained by these movements 



VOL. XI. rAT II. 



of this fish has not been ascertained, nor has even a Structure 

 conjecture been offered on the subject. aRtl 



The organs of motion, we have already hinted, are ofFi&hcs." 

 extensively employed by the systematic ichthyologist in -_r- y ^ 

 the formation of his divisions. It does not appear, how- 

 ever, that naturalists have determined the exact value 

 of the characters which they furnish, either for generic 

 or specific distinctions. La Cepede, in some instances, 

 has formed genera from a difference in the number of 

 the dorsal fins ; while into the genus Gadus, species with 

 one, two, and even three fins, are admitted. As the 

 number of the fins is invariably the same in the same 

 species, and as these organs may be supposed to exer- 

 cise considerable influence on the habits of fishes, the 

 character thus exhibited may be safely employed in 

 generic distinctions. The characters furnished by the 

 structure of the fins have not been overlooked, especial- 

 ly the rays. The circumstance of being bony or joint- 

 ed, is often noticed in specific distinctions, although 

 well entitled to regulate divisions of a higher kind, as 

 the character furnished is permanent. Those charac- 

 ters furnished by the fins, which are employed exclu- 

 sively in the construction of species, are derived from 

 their form, and the number of their rays. But as these 

 characters are liable to vary in different individuals of 

 the same species, they should be employed with great 

 caution. In many fishes there are numerous rays on 

 each side the different fins so concealed under the skin, 

 that it is impossible to count them, while others do not 

 reach the extremity of the organ. Hence the number 

 of rays must vary with the mode of enumerating, and 

 perhaps with the age of the animal. The extent of va- 

 nation occasioned by the last cause has not been sa- 

 tisfactorily determined. 



SECT. V. Organ of Adhesion. 



THE organ here referred to, generally termed tucker, Organ of 

 is only found on a few fishes. In some of these it is adhesion. 

 situated on the upper part of the head, while in others 

 it is placed on the thorax. In the celebrated fish call- 

 ed the Remora, it is of an oval form, and consists of 

 transverse rows of cartilaginous plates, connected by 

 one edge to the surface of the head, and in the other 

 edge free, and finely pectinated. A longitudinal par- 

 tition divides the plates in the middle of the head. In 

 the spaces between the plates, and on each side of the 

 partition, a row of fleshy tubercles may be observed. In 

 the cyclopteri this organ is of a circular form, and con- 

 sists of numerous soft papillae. It is situated on the 

 thorax. Instead of a separate organ of adhesion, the 

 ventral fins in the goby are united, and are capable of 

 adhering to rock* and stones, while in the lampry the 

 mouth contracts and acts as a sucker. 



The existence of a sucker is equally common to some 

 cartilaginous and osseous fishes. Its use to the fish is 

 difficult to ascertain. When, by means of this organ, 

 the fish attaches itself to the sides of other fishes, or to 

 the bottom of ships, it is carried forward without any 

 exertion of its own ; and, during storms, adhesion to 

 rocks by means of it, may save a weak fish from being 

 tossed about !>y the fury of the waves ; but there may 

 perhaps be other purposes to which it is subservient, 

 which still remain to be discovered. 



1'he sucker furnishes to the ichthyologist characters 

 for the discrimination of the species which are obvious 

 and permanent ; but these have seldom been describeU- 

 with accuracy or minuteness. 



