THE REASON WHY IN NATURAL HISTORY. 



FISHES. 





109. Why have fishes fins f 



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. 



no. 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 sur- 

 face to elevate it or guide it. 



in. Why have fishes scales ? 



Because scales, while they afford protection 

 to the bodies of fish, are conveniently adapted to 

 their motions ; and as the scales present no sur- 

 face to obstruct their passage through the water, 

 as hair or feathers would do, they evidently form 

 the best covering for the aquatic animal. 



112. Why do fishes float in streams (when they 

 are not swimming) with their heads toward the 

 stream 9 



Because they breathe by the transmission of 

 water over the surface of their gills, the water 

 entering at the mouth, and passing over the gills 

 behind. When, therefore, they lie motionless 

 with their heads to the stream, they ar in that 

 position which naturally assists their breathing 

 process. 



113. Why have fishes air-bladders 1 



Because, as the density of water varies greatly 

 at different depths, the enlargement or contrac- 

 tion of the bladder regulates the relation of the 

 specific gravity of the body of the fish to that of 

 the water in which it moves. 



114. Why have whales a very large development 

 efoily matter about their heads t 



Because their heads are thereby rendered the 

 lighter part of their bodies, and a very slight 

 exertion on the part of the animal will bring its 

 head to the surface to breathe air, which it con- 

 stantly requires. 



115. Why have mussels strong, tendinous threads 

 proceeding from their shells t 



Because as they live in places that are beaten 

 by the surf of the sea, they moor their shells by 

 those threads to rocks and timbers. 



1 1 6. Why have cockles stiff, muscular tongues t 

 Because, having no threads to moor themselves, 



as the mussels have, they dig out with their 

 tongues a shelter for themselves in the sand. 



117. Why has the whale feathery-like lamina oj 

 whale-bone extending from its jaws ? 



Because these feathery bones, lying side by 

 side, form a sieve, or strainer, for the large 

 volumes of water which the whale receives into 

 its mouth, drawing off therefrom millions of smal 

 animals, which form a jelly-like mass upon which 

 the whale feeds. A whale has been known to 

 weigh as much as 249 tons, and its blubber 

 yielded 4,000 gallons of oil. How many millions 

 of living creatures must have gone to make up that 

 enormous mass of animal matter ! 



1 1 8. Why does not the iris of the fish's eye con- 

 tract ? 



Because the diminished light in water is never 

 too strong for the retina. 



119. Why is the eye of the eel covered with a 

 transparent horny covering 9 



Because as the eel lives in holes, and pushes 

 its head into mud, and under stones, etc., it 

 needed such a covering to defend the eye. 



1 20. Why is the whale provided with an eyt 

 having remarkably thick and strong coats ? 



Because, when he is attacked by the sword-fish 

 and the shark, he is almost helpless against his 

 enemies, as they fix themselves upon his huge 

 carcass. He therefore dives with them down 

 to a depth where the pressure of the water is so 

 great that they cannot bear it. The eye of the 

 whale is expressly organized to bear the immense 

 pressure of extreme ocean depths, without im 

 pairing the sight. 



121. Why have fishes no eyelids t 



Because the water in which they swim keeps 

 their eyes moist. Eyelids would therefore be 

 useless to them. 



122. Why have fishes the power of giving their 

 eye-balls very sudden motion t , 



