In this way, too, small variations of no selective
value may gradually increase until they chance to have a value to
the animal.*
* For a strong statement of the new critical position see Dewar
and Finn's "Making of Species," 1909, ch. vi.
The origin of the metamorphosis, or pupa-stage, of the higher
insects, with all its wonderful protective devices, is so obscure
and controverted that we must pass over it. Some authorities
think that the sleep-stage has been evolved for the protection of
the helpless transforming insect; some believe that it occurs
because movement would be injurious to the insect in that stage;
some say that the muscular system is actually dissolved in its
connections; and some recent experts suggest that it is a
reminiscence of the fact that the ancestors of the metamorphosing
insects were addicted to internal parasitism in their youth. It
is one of the problems of the future. At present we have no
fossil pupa-remains (though we have one caterpillar) to guide us.
We must leave these fascinating but difficult problems of insect
life, and glance at the evolution of the birds.
To the student of nature whose interest is confined to one branch
of science the record of life is a mysterious Succession of
waves.
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