Darwinism stated by Darwin himself: Characteristic passages from the writings of Charles DarwinDarwin, Charles
Science
Darwinism stated by Darwin himself: Characteristic passages from the writings of Charles Darwin
Darwin, Charles
Evolution (Biology)
The second objection, which has been insisted on by Delpino, is that
the tissues, for instance, of a mature salamander or crab, of which
a limb has been removed, are already differentiated and have passed
through their whole course of development; and how can such tissues in
accordance with our hypothesis attract and combine with the gemmules of
the part which is to be reproduced? In answer to these two objections
we must bear in mind the evidence which has been advanced, showing
that at least in a large number of cases the power of regrowth is a
localized faculty, acquired for the sake of repairing special injuries
to which each particular creature is liable; and, in the case of buds
or fissiparous generation, for the sake of quickly multiplying the
organism at a period of life when it can be supported in large numbers.
These considerations lead us to believe that in all such cases a stock
of nascent cells or of partially developed gemmules are retained for
this special purpose either locally or throughout the body, ready to
combine with the gemmules derived from the cells which come next in due
succession. If this be admitted, we have a sufficient answer to the
above two objections. Anyhow, pangenesis seems to throw a considerable
amount of light on the wonderful power of regrowth.
EFFECT OF MORBID ACTION.
[Page 392.]
We have as yet spoken only of the removal of parts, when not followed
by morbid action: but, when the operation is thus followed, it is
certain that the deficiency is sometimes inherited. In a former chapter
instances were given, as of a cow, the loss of whose horn was followed
by suppuration, and her calves were destitute of a horn on the same
side of their heads. But the evidence which admits of no doubt is
that given by Brown-Séquard with respect to Guinea-pigs, which, after
their sciatic nerves had been divided, gnawed off their own gangrenous
toes, and the toes of their offspring were deficient in at least
thirteen instances on the corresponding feet. The inheritance of the
lost part in several of these cases is all the more remarkable as only
one parent was affected; but we know that a congenital deficiency is
often transmitted from one parent alone--for instance, the offspring
of hornless cattle of either sex, when crossed with perfect animals,
are often hornless. How, then, in accordance with our hypothesis can
we account for mutilations being sometimes strongly inherited, if they
are followed by diseased action? The answer probably is that all the
gemmules of the mutilated or amputated part are gradually attracted
to the diseased surface during the reparative process, and are there
destroyed by the morbid action.
TRANSMISSION LIMITED.
[Page 396.]
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