CHAPTER VIII
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VARIATION AND DIFFERENTIATION OF FISHES
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IT is a common saying, that no two peas are ever quite alike,
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and in no group of Vertebrates is this fact more manifest‘
than among the shes.
The characters that later become
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more or less xed, such as the head and number of vertebræ,
show here. a refharkable amount of variation.
Fishes stand '
at the beginning of the Veftebrate series, and their greater
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variability ”is connected with their low constitutional level
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and Closer contact With the environmental inuences.
For
these reasons the studyof variation in shes is of peculiar
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interest…
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I. NATURE OF VARIATION
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Fishes differ greatly in size and shape, and according to
their habits and habitats, but by variation is meant some—
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thing more precise than these di”erenceS,
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The tennis used
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here as Darwin used it, to express…the
differences
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between individuals of the same
These
variations - provided thePmaterialë,gDarwin =thought, for
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Natural Selection toc—wqu=,upôhL—flf any advance has
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been made Since
t1me1nou1 way of regarding
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variations, it-has comefrom ?ëndeavours to trace their causes
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had-td be èjq-tenïtwith accepting them as chance
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In this way the study of varia-’
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tions has become
as precise in its methods
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Ïand
the physical sciences. Its
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for;thè
biological problems has perhaps been
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j”estimatedtofdhighly, but,—there Canbe no doubt thatit is
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