ICHTHYOLOGY. 



-inn-lure While others, even under water, as the salmon, utter 

 ami certain sounds while in the act of depositing their 

 s spawn; but for what purpose these sounds are uttered, 

 "__ K '^'. or by what organs they are produced, we are still ig- 

 norant. 



SECT. IV. Organs of Motion. 



Organs of IF we attend to the vast variety of forms, exhibited 

 motion. by different kinds of fish, we shall be disposed to con- 

 clude that shape exercises but little influence on their 

 movements. While some are cylindrical and lengthen- 

 ed, others are nearly globular: some are depressed, 

 while others are compressed. The general form, how- 

 ever, approaches to ovate, the body being thickest at 

 the thorax, and tapering a little towards the head and 

 tail. 



The fins of fishes, correspond with the wings of birds, 

 the former being calculated to give the motion to the 

 body in the water, the latter in the air. These organs 

 vary in number, size, situation, and structure, in dif- 

 ferent species. 



The number of fins varies according to the genera, 

 and even according to the species. It is difficult to fix 

 on those fins which exercise the greatest influence on 

 the habits of the animal, as there is not any one fin 

 common to all fishes, although all fishes have at least 

 one of these organs. The size of the fins is equally va- 

 rious in the different species, as it bears no constant 

 proportion to the figure or magnitude of the fish, nor to 

 its habits or instincts. 



The situatian of the fins furnishes the ichthyologist 

 with some of the most obvious and useful characters. 

 Those fins which are situated on the back are termed 

 dorsal, and vary greatly in number and shape. The 

 fin which surrounds the extremity of the tail, is termed 

 the caudal fin, and is always placed perpendicularly. 

 It is forked in some, even, or rounded in others. Be- 

 tween the caudal fin and the anus are situated the anal 

 fins, which vary in number and shape according to the 

 species. Between the anus and throat are placed the 

 ventral fins. When they do exist, they never exceed 

 two in number, and are parallel to each other. The 

 pecloraljiiis are usually two in number, and are placed 

 on each side, a short way behind the gill opening. By 

 Linnaaus and others, the ventral fins are considered as 

 v analogous to the feet of quadrupeds, and the characters 



furnished by their position are employed as the basis 

 of his classification. Those fishes which are destitute 

 of ventral fins, are termed, in his system, apodal;]t.hose 

 which have the ventral fins placed nearer to the ante- 

 rior extremity than the pectoral fins, are termed jugu- 

 lar ; those having the ventral fins beneath the pectoral, 

 he calls thoracic, and when the ventral fins are placed 

 behind the pectoral fins they are termed abdominal. 

 These distinctions are of great importance in an artifi- 

 cial system, and may be employed with success in the 

 inferior divisions of a natural one. 



The structure of the fins of fishes has long occupied 

 the attention of naturalists. In general these organs 

 consist of numerous jointed rays, which are subdivided 

 at their extremities. These are covered on each side 

 by the common integuments, which form in some in- 

 stances soft fibres projecting beyond the rays. These 

 fins, with articulated rays, were considered by the older 

 ichthyologists as furnishing characters for arrangement 

 of great importance. Fishes possessing these were 

 termed malacopterygii. Besides these articulated rays, 

 there exist in the fins of some fishes, one or more rays 



made up of a single bony piece, enveloped like the for- 

 mer by a common membrane. Some fishes have one 

 or more fins consisting entirely of these bony rays. 

 Fishes with such rays are termed acnnthopterygii. In 

 a few genera the posterior dorsal fin is destitute of rays, 

 and has obtained the name of pinna adiposa or flesh- 

 fin. 



As these rays serve to support the fins, and are 

 capable of approaching or separating like the sticks of 

 a fan, we may conclude that they move upon some 

 more solid body as a fulcrum. Accordingly we find in 

 the sharks, for example, that the rays of the pectoral 

 fins are connected by a cartilage to the spine. In the 

 osseous fishes the pectoral fins are attached to an osseous 

 girdle which surrounds the body behind the branchiae, 

 and which supports the posterior edge of their aperture. 

 This osseous girdle is formed of one bone from each 

 side, articulated at the posterior superior angle of the 

 cranium, and descending under the neck, where it unites 

 with the corresponding bone. Between the rays of the 

 fin and this bone, which resembles the scapula, there is 

 a range of small flat bones separated by cartilaginous 

 intervals, which may be compared to the bones of the 

 carpus. The rays of the ventral fins are articulated to 

 bones which correspond to the pelvis in the higher 

 classes of animals. The pelvis is never articulated with 

 the spine, nor does it ever form an osseous girdle round 

 the abdomen. In the jugular and thoracic fishes it is 

 articulated to the base of the osseous girdle which sup- 

 ports the pectoral fins. In the abdominal fishes, the 

 bones of the pelvis are never articulated to the osseous 

 girdle, and are seldom connected with each other. 

 They are preserved in their situation by means of cer- 

 tain ligaments. The rays of the caudal fin are articu- 

 lated with the last of the caudal vertebrae, which is in 

 general of a triangular form and flat. The rays of the 

 dorsal fin are supported by little bones, which have the 

 same direction as the spinous processes, and to which 

 they are attached by ligaments. 



As connected with the fins, we may here take notice 

 of those organs which are termed cirri or tentacula, ac- 

 cording as they are placed about the mouth, or on the 

 upper part of the head. They are in general sort, but 

 often contain one jointed ray. They do not differ in 

 structure from the fins, and are so closely connected 

 with them, that it is difficult to point out their use. It 

 is not probable that they are organs of touch, but ra- 

 ther peculiar modifications of fins. 



The muscles which move the fins, and all the other 

 organs of the body, are of a paler colour than in the ani- 

 mals of a higher order. They are also more uniform in 

 their substance, being in general destitute of tendinous 

 fibres. In the greater number of fishes there are no 

 muscles peculiar to the head. The sides are furnish- 

 ed with the most powerful ones, to execute the lateral 

 movements of the animal. These muscles are disposed 

 in layers or arches, with the convexity towards the 

 head. The different muscles are strengthened by small 

 detached spines, imbedded among the fibres of the 

 muscle, and giving them additional strength. Between 

 the layers there is in general a quantity of viscid albu- 

 minous matter interposed. After death this fluid speed- 

 ily undergoes a change, and can seldom be observed in 

 fishes which have been kept a few days. But in re- 

 cent fish, when boiled, the albumen appears coagulated 

 in the form of white curd between the layers of the 

 lateral muscles. 



The motions of a fish are performed by means of its 

 fins. The caudal fin is the principal organ of progres- 



Structuii 



and 



Function 

 of Fishei 



