342 ZOOLOGY. 



and fins, varies. Finally, the hyoid apparatus supporting 

 the gills is arranged pretty much as in other fishes, but in 

 the last of the series, the lampreys, the branchial arches are 

 wanting. 



482. Most fish swim with great agility, and it is said 

 that the salmon goes at the rate of twenty-four feet in a 

 second. They swim by alternate flexions of the tail and 

 trunk, and the muscles intended to move these form the 

 greater part of the mass of the body. The lateral fins are 

 not much used in progression, and seem merely intended to 

 maintain the equilibrium of the body, or slightly to modify 

 the direction of its course. 



483. A remarkable feature in the organization of some 

 fish is the swimming bladder, placed in the abdomen under 

 the dorsal spine, communicating often with the gullet or 

 stomach by a canal, permitting of the escape of air from its 

 interior ; but sometimes no such passage exists, and then it is 

 evident that the air contained in the swimming bladder is 

 a secretion from a gland situated on its walls. By the 

 movement of the ribs, this air bladder is acted on, so that by 

 the quantity of air being diminished, the specific gravity of the 

 fish alters according to circumstances ; but fish swimming 

 near the bottom have no air bladder such as the skate, sole, 

 turbot, and eel ; and sometimes this bladder is membranous 

 and vascular, so as to resemble a lung. 



In a small number of fishes, as the flying fish, the pectoral 

 fins are much extended, so as to permit the animal to leave 

 the waters and to fly to a considerable distance ; and some 

 by the same means travel on the land, and even climb 

 up trees. 



Whilst speaking of the organs of motion in fishes, we 

 cannot omit mentioning a singular apparatus which some of 

 these animals have, by means of which they adhere strongly 

 to a foreign body : it is a flattened disc covering the top of 

 the head, composed of cartilaginous plates, moveable, and di- 

 rected obliquely backwards (Fig. 312). Fishes of the genus 

 echeneis are the only ones which have this kind of organiza- 

 tion, and the species found in the Mediterranean has been 

 long celebrated under the name of remora (Fig. 313). Its 

 natural history has been overloaded with fables, and the 

 power of suddenly arresting a ship in its course was ascribed to 

 it. A species closely resembling the preceding is very common 

 in the waters around the Isle of France, and it is said that 



