So you see that the home of the fish is perfectly suited to it. In the
aquarium you would observe that while most of the fishes dart hither and
thither, there are some which never rise to the surface of the water. These
are the flat-fish; and they keep at the bottom, because for some wise
purpose God has made them without the power of rising and sinking like
others.
Inside most fishes there is a bag filled with air, as is the india-rubber
ball which you delight to bounce so high. The fish can make this little
balloon larger or smaller, just as it wishes to be itself lighter or
heavier. As it swims along, it is usually about the same weight as the
water; but when it wants to dive, the fish squeezes its air-bag tightly
together, which causes its body to become heavier than the water--for air
pressed closely together becomes heavy, and its own weight sinks it down.
When it wants to rise again to the surface, it ceases to squeeze this bag,
the air in the little balloon expands, and the diver rises again and floats
or swims because its body is now lighter than the water.
Is not this a very perfect and beautiful plan? How true it is that God has
provided for the wants of all His creatures, and fitted them for the life
designed for them!
But besides rising or sinking when they please, fishes can turn themselves
about very quickly. To understand how they do this, you must look at the
long bone which runs right through the body, from head to tail.
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