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THE FOURTH CLASS OF A'ERTEBRATED ANIMALS. 

 THE FISlIES^(P/.S't'i?.S'). 



[Fishes are the jiroper vertebratcd inhabitants of the waters ; anJ they are formed 

 ana organized for living, moving, and in general finding their food, wholly within this 

 element. The nature of their locality necessarily makes their history obscure, because 

 human observation extends to only a very limited portion of the waters, and in that 

 portion to only a trifling depth ; but when we consider that, exclusive of lakes and 

 rivers, the seas occupy fidl seven-tenths of the earth's surface, that those seas yield 

 food as far down as the rays of the sun can extend their life-giving energy, and that 

 there is no obstacle in the water to bar the motions of the fish, we can at once see 

 that, of all vertebrated animals, they must be the most numerous, and probably they 

 exceed in numbers the whole of the other three classes of the same grand division of 

 animated nature. They inhabit, stratum super stratum, as it were, — one species near 

 the surface, another near the bottom, and others, again, range through the intermediate 

 depth. What may be the absolute depth of the ocean waters at which life ceases, and 

 the profound of death and darkness begins, we have no direct means of ascerttdning. 

 It varies, of course, with the latitude, being greater as the rays of the sun are more 

 direct, and less as their obliquity increases ; and it probably also varies with the nature 

 of the bottom. In correspondence with the vast range of pasture which is assigned to 

 the Fishes, their productive powers are enormous, — the young produced by one Cod-fish, 

 at a single deposit, being ascertained to be not much less than four millions, while in the 

 common Flounder they are not fewer than one hundred and fifty thousand. A fertility 

 so enormous, as compared with anything we are acquainted with on land, of itseh' 

 shows the importance of the Class, and how well they are adapted for supplying each 

 other with food. But, interesting as it is, the space to which we are restricted, forbids 

 any disquisition on their physiology; and all that we can accomplish, is to render the 

 text of the last edition of Cuvier's great work, as faithfully in substance, and as briefly 

 in expression, as we possibly can. Our own original remarks must necessarily be few; 

 and we shall inclose tbem in brackets, the same as this introductorj^ paragrajih, to dis- 

 tinguish them from the substantive part of the genuine text of Cuvier, which, in the 

 way of systematic arrangement, has received no improvement, since the science of 

 Zoology was deprived of that foremost of its cultivators.] 



Fishes are oviparous Vertebrata, with a double circulation, and respiring through the 



medium of water. For this purpose they have, on each side of the neck, branchia?, or 



gills, consisting of arches of bone attached to the os lujoides, or bone of the tongue; 



and to these arches the filaments of the gills are attached, generally in a row upon 



each, and having their surfaces covered b)' a tissue of innumerable blood-vessels. The 



water taken in by the mouth passes through among the filaments of the gills, and 



escapes by the gill-openings towards the rear. In its progress through the filaments 



of the gills, the water imparts to these the oxygen of the air which it contains [and 



receives carbon in return, the same as in the lungs of an air-breathing animal. The 



grils of a fish do not decompose water, so as to derive oxj'gen from it, but mcrelr scpa- 



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