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1859
1860
1861
1866
1869
1872

Compare with:
1859
1860
1866
1869
1872

An organ, 1859 1860 1861 1866 1869
Organs, originally formed by the aid of natural selection, 1872

when 1859 1860 1861 1866 1872
originally formed by the aid of natural selection, when 1869

1 blocks not present in 1859 1860 1861 1866 1869; present in 1872
All this agrees well with what we see under nature.

to 1859 1860 1861 1866
has to exert 1869 1872

reproduce 1859 1860 1861 1866 1869
tend to reproduce 1872

age, and consequently 1859 1860 1861
age, but 1866
mature age, but 1869 1872

relative size of rudimentary organs in the embryo, 1859 1860 1861 1866
size of rudimentary organs in the embryo relatively to its other parts, 1869
size of rudimentary organs in the embryo relatively to the adjoining parts, 1872

(as we have good reason to believe 1859 1860 1861 1866
the rudimentary part would tend 1869

possible), the rudimentary part would tend to be 1860 1861 1866
possible) the rudimentary part would tend to be 1859
OMIT 1869

economy, 1859 1860 1861
economy 1866
the economy of organisation, 1869

explained in 1859 1860 1861 1869
in organisation, explained in 1866

will probably often 1859 1860 1861 1866
may often have 1869

this will tend to cause 1859 1860 1861 1866
aided in 1869

As the presence of 1859 1860 1861 1866 1869
Finally, as 1872

is thus due to the tendency in every part of the organisation, which has long existed, to be 1859 1860 1861 1866 1869
by whatever steps they may have been degraded into their present useless condition, are the record of a former state of things, and have been retained solely through the power of 1872

have 1859 1860 1861 1866 1869
in placing organisms in their proper places in the natural system, have often 1872

An organ, when rendered
useless
useless,
may well be variable, for
their
its
variations
can no
cannot
longer be
be
checked by natural selection.
Moreover, at
At
whatever period of life
either disuse
disuse
or selection reduces an organ, and this will generally be when the being has come to maturity and to its full powers of action, the principle of inheritance at corresponding ages will reproduce the organ in its reduced state at the same age, and consequently will seldom affect
or reduce
or reduce
it in the embryo. Thus we can understand the greater relative size of rudimentary organs in the embryo, and their lesser relative size in the adult. But if each step of the process of reduction were to be inherited, not at
a
the
corresponding age, but at
a very
an extremely
early period of
life,
life
(as we have good reason to believe to be possible), the rudimentary part would tend to be wholly lost, and we should have a case of complete abortion. The principle, also, of economy, explained in a former chapter, by which the materials forming any
part,
part
or structure,
or structure,
if not useful to the possessor, will be saved as far as is possible, will probably often come into
play,
play;
and this will tend to cause the entire obliteration of a rudimentary organ.
As the presence of rudimentary
organs,
organs
is thus due to the tendency in every part of the organisation, which has long existed, to be
inheritance,—
inherited—
we can understand, on the genealogical view of classification, how it is that
systematists,
systematists
have found rudimentary parts as useful as, or even sometimes more useful than, parts of high physiological importance. Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue
in seeking
in seeking
for its derivation. On the view of descent
with,
with
modification, we may conclude that the existence of organs in a rudimentary, imperfect, and useless condition, or quite aborted, far