PISCES. 



thus becoming opaque. In the eye of 

 the skate tribe there is a digitated cur- 

 tain, which hangs over the pupil, and 

 which may shut out the light when the 

 animal rests, being somewhst similar to 

 the tunica adnata of other animals." 



We now proceed to notice the motion 

 of fishes, for the celerity of which their 

 shape is admirably adapted : hence, ves- 

 sels designed to be navigated in water 

 are made to imitate, in some degree or 

 other, the shape offish ; but the rapidity 

 of a ship in sailing before the wind is not 

 to be compared to the velocity of a fish. 

 The largest fishes are known to overtake 

 a ship in full sail with the greatest ease, 

 to play round it without effort, and to 

 surpass it at pleasure. Every part of the 

 body seems formed for dispatch .- the 

 fins, the tail, and the motion of the whole 

 back-bone assist in the business ; and it 

 is to that flexibility of body which mocks 

 the effort of art, that fishes owe the great 

 velocity of their motions. The chief in- 

 struments in a fish's motion are its fins, 

 air-bludder and tail ; with two pair, and 

 three single fins, it will migrate a thou- 

 s^nd leagues in a season, and without in- 

 dicating any visible symptoms of languor 

 or fatigue. The fins serve not only to 

 assist the animal in progression, but in 

 rising and sinking, in turning, and even 

 in leaping out of the water. The pecto- 

 ral fins serve to push the animal forward, 

 and to balance the head when it is too 

 large for the body, and prevent it from 

 tumbling to the bottom, which it infalli- 

 bly would if the fins were cut off. The 

 ventral fins, which always lie flat in the 

 water, serve rather to raise or depress, 

 the body, than to assist its progressive 

 motion. The dorsal fin acts as a poiser, 

 in preserving the animal's equilibrium, 

 while it aids the forward movement ; and 

 the anal fin is designed to maintain the 

 vertical position of the body. By means 

 of the air bladder, fishes can increase or 

 diminish the specific gravity of their body. 

 When they contract it, and press out the 

 air, the bulk of the body is diminished, 

 and the fish sinks as far as it pleases : on 

 relaxing the operation, the bladder ac- 

 quires its natural size, the body becomes 

 specifically lighter, and the fish is ena- 

 bled to swim near the surface. The tail, 

 in the last place, may be regarded as the 

 rudder, directing the motions of the 

 fish, to which the fins are only subser- 

 vient. 



With respect to the nourishment of 

 fishes : they are mostly carnivorous, 

 though they seize upon almost any thing 



that falls in their way, and not uncommon- 

 ly devour their own offspring : they 

 seem, indeed, to manifest a particular 

 predilection for whatever they can swal- 

 low possessed of life. They often njeet with 

 each other in fierce opposition, and the 

 victor, without scruple, devours his anta- 

 gonist. Thus are they irritated by the 

 continual desire of satisfying their hun- 

 ger ; and the life of a fish, from the small- 

 est to the greatest, is but one scene of 

 hostility and violence. The smaller spe- 

 cies, which stand no chance in the un- 

 equal combat, resort to those shallows 

 where the larger are unable to approach. 

 There they become invaders in their 

 turn, and live on the spawn of large fishes, 

 and on small insects and worms, which 

 they find floating on the water. Fishes 

 can, however, notwithstanding their na- 

 tural voracity, live long, apparently, with- 

 out food ; but they, perhaps, in vases and 

 other ornamental vessels, feed on insects 

 too small for the human eye to see ; or, it 

 has been thought, they may have the 

 power of chemically decomposing water. 

 We now proceed to the subject of repro- 

 duction. 



In most, if not in all fishes, there is a dif- 

 ' ference in sex, though Bloch and others 

 make mention of individuals, which seem- 

 ed to unite the two sexes, and to be real 

 hermaphrodites. The number of males, 

 it has been remarked, is about double 

 that of females ; and were it not for this 

 wise provision of nature, a large propor- 

 tion of the extruded eggs would remain 

 unfecundated. A few species, indeed, as 

 the eel, blenny, &,c. are viviparous; but 

 by far the greater number are produced 

 from eggs. These last compose the roe, 

 ovaries of the females, which lie along 

 within the abdomen. The milt of the 

 males is disposed along the back-bone, in 

 one or two bags, and consists of a whitish 

 glandular substance, which secretes the 

 spermatic fluid. Though the history of 

 the generation of fishes be still involved 

 in considerable obscurity, it seems to be 

 ascertained, that no sexual union takes 

 place among the oviparous kinds, and 

 that the eggs are fructified after exclu- 

 sion. They are of a spherical form, and 

 consist of a yolk, a white part, and a 

 bright crescent-like spot, or germ. The 

 yolk, which is usually surrounded by the 

 white, is round, and not placed in the 

 middle, but towards one of the sides ; and 

 the clear spot, or embryo, is situated be- 

 tween the yolk and the white. 



In this spot there is observable, on the 

 day after fecundation, a moveable point, 



