Fig. 68.—PERCH.
The fins of fishes are to them, what wings and tails are to birds, enabling them to rise in the fluid in which they live by the reaction of the motions of the fins upon its substance.
"Speak to the earth, and it shall teach thee; and the fishes of the sea shall declare unto thee. Who knoweth not in all these that the hand of the Lord hath wrought this."—Job xii.
1054. Why are the fins of fishes proportionately so much smaller than the wings of birds?
Because there is less difference between the specific gravity of the body of a fish, and the water in which it moves, than between the body of a bird, and the air on which it flies. The fish, therefore does not require such an expanded surface to elevate or guide it.