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and become gradually 1859 1860 1861 1866
becoming at the same time 1869 1872

to any extent, 1859 1860 1861 1866
OMIT 1869 1872

this great amount of modification there would be no tendency 1866
this great amount of modification there will be no tendency 1859 1860 1861
this modification would not tend 1869
these modifications would not tend 1872

the ancient progenitor, 1859 1860 1861 1866
an early progenitor,— 1869
an early progenitor— 1872

had 1859 1860 1861 1866 1869
birds, and reptiles, had 1872

will 1859 1861 1866 1869 1872
acting on some originally created form, will 1860

to have been 1859 1860 1861 1866
OMIT 1869 1872

a certain extent 1859 1860 1861 1866
have been partially 1869
have become partially 1872

the comparison not 1859 1860 1861 1866 1869
serial homologies, or the comparison 1872

or organ in different members of the same class, but 1866
in different members of a class, but 1859 1860 1861
or organs in different members of the same class, but 1869
or organs in the same individual, and not 1872

the same individual. 1859 1860 1861 1866 1869
different members of the same class. 1872

bones of a limb might be shortened and
flattened
widened
to any extent, and become gradually enveloped in thick membrane, so as to serve as a fin; or a webbed
hand
foot
might have all its bones, or certain
bones
bones,
lengthened to any extent,
with
and
the membrane connecting them
increased,
increased
to any extent, so as to serve as a
wing:
wing;
yet
in
in
all this great amount of modification there would be no tendency to alter the framework of
bones
the bones
or the relative connexion of the
several
several
parts. If we suppose that the ancient progenitor, the archetype as it may be
called,—
called—
called,
of all mammals, had its limbs constructed on the existing general pattern, for whatever purpose they served, we can at once perceive the plain signification of the homologous construction of the limbs throughout the
whole
whole
class. So with the mouths of insects, we have only to suppose that their common progenitor had an upper lip, mandibles, and two
pairs
pair
of maxillæ, these parts being perhaps very simple in form; and then natural
selection,
selection
will account for the infinite diversity in
the structure
structure
and
functions
function
of the mouths of insects. Nevertheless, it is conceivable that the general pattern of an organ might become so much obscured as to be finally lost, by the
reduction
atrophy
and ultimately by the complete abortion of certain parts, by the
fusion
soldering together
of other parts, and by the doubling or multiplication of others,—
varia- tions
variations
which we know to be within the limits of possibility. In the paddles of the
gigantic extinct
extinct gigantic
sea-lizards, and in the mouths of certain suctorial crustaceans, the general pattern seems to have been thus to a certain extent obscured.
There is another and equally curious branch of
our present
our
the present
subject; namely, the comparison not of the
different
same
parts
part
or organ in different members of the same class, but of the
same
different
parts or organs in the same individual. Most physiologists believe that the bones of the skull are