Therefore it seems hardly credible
that the co-ordinated erection of the dermal appendages,
by which the animal is made to appear larger and more terrible
to its enemies or rivals, should be altogether an incidental
and purposeless result of the disturbance of the sensorium.
This seems almost as incredible as that the erection by
the hedgehog of its spines, or of the quills by the porcupine,
or of the ornamental plumes by many birds during their courtship.
should all be purposeless actions.
[18] `Lehrbuch der Histologie des Menschen,' 1857, s. 82. I owe
to Prof. W. Turner's kindness an extract from this work.
[19] `Quarterly Journal of Microscopical Science,' 1853, vol. i. p. 262.
We here encounter a great difficulty. How can the contraction of
the unstriped and involuntary _arrectores pili_ have been co-ordinated
with that of various voluntary muscles for the same special purpose?
If we could believe that the arrectores primordially had been
voluntary muscles, and had since lost their stripes and become involuntary,
the case would be comparatively simple. I am not, however, aware that
there is any evidence in favour of this view; although the reversed
transition would not have presented any great difficulty,
as the voluntary muscles are in an unstriped condition in the embryos
of the higher animals, and in the larvae of some crustaceans.
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