Perhaps if you think of a fish and a bird--say a herring and a sparrow--you
will say two creatures could hardly be less like each other; the bird has
soft warm feathers, and the fish has scales, overlapping each other as the
slates on the roof of a house do, thus making a perfectly waterproof coat
for its whole body; the bird has legs and wings, and the fish has neither;
the bird can chirp and sing, while fishes generally make no noise.
But if you could look inside the feathers and the scales, you would
see that there is a likeness in the bony structure of these creatures,
otherwise so unlike. Both are vertebrate animals, though the backbone of
a fish is in some respects unlike that of a bird, still the _plan_ is the
same, and it has been truly said that "among the many wonders of nature
there is nothing more wonderful than this--the adaptability of the one
Vertebrate type to the infinite variety of life to which it serves an as
organ and a home." But when you said that the herring had neither legs nor
wings, you forgot to notice the fins, by means of which it moves from place
to place in its watery home; as the bird, on its strong wings, makes its
way through the fields of air. Birds too, lay eggs, and so do most fishes,
some of them even making nests; so there are points in which they resemble
each other, are there not?
But while we know a good deal about the ways and habits of birds, very
little is known of the life of a fish; for it is much more difficult to
watch its way of living, and what is known about animals has been learned
by watching them patiently.
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