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LEFT FISH 141 FISH contained in that element. As the water in contact with the gills becomes de- teriorated, it is necessary that a constant current be caused to Aov/ over them. In most fishes this is effected by their tak- ing water in at the mouth and expelling it at the gill-covers. The blood, which is con- stantly sent from the gills to the heart, is distributed by means of the arteries to every part of the body, whence it returns to the heart by means of the veins. Ani- mals of this order are for the most part furnished with an air-bladder in the in- terior of the body, which, as it is often connected with the oesophagus by a tube, must be regarded to a certain extent analogous to the lungs of the air breath- ing Vertebrata. This sac or air bladder, however, has nothing to do with respira- tion; it receives blood from the arteries, and I'eturns it into the veins and the air which it incloses is probably derived from this fluid. By the dilatation or com- pression of this sac, the specific gravity of the fish is governed, and, acted on by a curious muscular apparatus, renders its possessor lighter or heavier than the surrounding element. The limbs of the fish are formed into fins; the forelegs constituting what are termed the pec- toral fins, and the posterior extremities, the ventral. Besides these, ordinary fishes are furnished with one or two dorsal fins, an anal fin, and a caudal fin, or tail. The principal organ of motion is the caudal fin, or tail; by this it is propelled. The dorsal and ventral fins serve to bal- ance it, and the pectorals to arrest its progress when required. The bones of fishes are of a less dense and compact nature than in the higher order of ani- mals, and always remain in an isolated state, similar to that of the embryo of the Mammalia. The head varies more in form than in any other class of verte- brate animals. The same bones as those found in other oviparous animals are al- most always traceable. The upper jaw consists of maxillary and intermaxillary bones. In the greater number of fishes, the intermaxillary bones constitute the chief portion of the upper jaw, the max- illary bones being placed behind and pa- rallel to them. The lower jaw is composed generally of two bones on each side, the dental portion in front, and the articular portion behind. The form of the body is for the most part such as mechanical principles teach to be best adapted for moving with least resistance through a liquid medium. The surface of the body is either smooth and lubri- cous, or is covered by closely imbricated scales, rarely defended by bony plates or roughened by hard tubercles, still more Vol. IV— Cyc— J rarely armed with spines. The power of touch can be but feebly developed in fishes. The organ of taste is a very in- conspicuous one — the chief function of the framework supporting it, or the hyoi- dan apparatus, relating to the mechan- ism of swallowing and breathing. Of the organ of hearing there is no outward sign; but the essential part, the acoustic labyrinth, is present, and the semicir- cular canal, largely developed within the labyrinth, is without cochlea, and is rarely provided with a special chamber, but is lodged, in common with the brain, in the cranial cavity. The eyes are usually large, but seldom defended by eyelids, and ever destitute of a lachrymal organ. The alimentary canal is commonly short and simple, with its divisions not always clearly marked, the short and Made gullet being hardly distinguishable from the stomach. The blood of fishes is red but cold, and is rarely elevated above the temperature of the surrounding ele- ment. The sexes of fishes, excepting the sharks and rays, offer no very decided external characters by which they may be distinguished. The respiratory organs, however, occupy more space in the males than in the females, and, on the other hand, the abdomen is larger in the females than in the males. The differences of character in the scales have been made the foundation of a classification of fishes by Agassiz, by whom all fishes are distributed into the following four orders of cycloid, ctenoid, placoid, and ganoid fishes, having respectively cycloid, ctenoid, placoid, and ganoid scales; a classification which has been found par- ticularly convenient with reference to fossil fishes. FISH, HAMILTON, an American diplomatist; born in New York City, Aug. 3, 1808; was graduated at Columbia College, and admitted to the bar in 1830. A Whig in politics, he was elected a congressman in 1842, and governor in 1848. In 1851 he was returned to the United States Senate, where he opposed the I'epeal of the Missouri Compromise and joined the Republican party on its formation. He was Secretary of State under Grant from 1869 to 1877, signing, as one of the commissioners, the Wash- ington Treaty of 1871, and carrying through the settlement of the "Alabama" question. Died at Garrison, Putnam CO., N. Y., Sept. 7, 1893. FISH, NICHOLAS, an American mili- tary officer; born in New York City, Aug. 28, 1758, studied law; joined the Continental army and was an aide on the staff of John Morin Scott early in