We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind. Numerous cases could be given amongst the lower animals of the same organ performing at the same time wholly distinct functions; thus
the alimentary canal respires, digests, and excretes the alimentary canal respires, digests, and excretes 1859 1860 1861 1866 1869 |
OMIT 1872 |
in the larva of the dragon-fly and in the fish
Cobites. Cobites. 1859 1860 1861 1866 1869 |
Cobites the alimentary canal respires, digests, and excretes. 1872 |
In the Hydra, the animal may be turned inside out, and the exterior surface will then digest and the stomach respire. In such cases natural selection might easily
specialise, if any advantage were thus gained, a part or
organ, which had
performed performed 1859 1860 1861 1866 | previously performed 1869 1872 |
two functions, for one function alone, and thus
greatly change its nature greatly change its nature 1866 |
wholly change its nature 1859 1860 1861 |
OMIT 1869 1872 |
by insensible
steps. steps. 1859 1860 1861 1866 |
steps greatly change its nature. 1869 1872 |
↑1 blocks not present in 1859 1860 1866 1869 1872; present in 1861 | Certain plants, as some Leguminosæ, Violaceæ, &c., bear two kinds of flowers; one having the normal structure of the order, the other kind being degraded, though sometimes more fertile than the perfect kind: if the plant ceased to bear its perfect flowers, and this did occur during several years with an imported specimen of Aspicarpa in France, a great and sudden transition would apparently be effected in the nature of the plant.
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Many cases are known of plants which regularly produce at different parts of their inflorescence, as on the summit of a spike and lower down, or at the centre and circumference of an umbel, corymb, &c., or during different periods of the year, differently constructed flowers; and if the plant were to cease producing both kinds and bore one alone, a great change would suddenly be effected in its specific character.
It
is a distinct question how is a distinct question how 1866 |
can also be shown that the production of the two sorts of flowers by 1869 |
is, however, probable that the two sorts of flowers borne by 1872 |
the same plant
has come to produce two kinds of flowers; but it can be shown in some cases to be probable, and in other cases to be almost certain, that this has been effected by finely graduated steps. has come to produce two kinds of flowers; but it can be shown in some cases to be probable, and in other cases to be almost certain, that this has been effected by finely graduated steps. 1866 |
has been effected by finely graduated steps. 1869 |
were originally differentiated by finely graduated steps, which may still be followed in some few cases.
1872 |
Again, two distinct
organs organs 1866 1869 | organs, 1872 |
in
the same
individual sometimes perform simultaneously individual sometimes perform simultaneously 1866 |
individual may simultaneously perform 1869 |
organ under two very different forms, may simultaneously perform in 1872 |
the same
function, function, 1866 1869 |
individual the same function, 1872 |
and this is
a highly a highly 1866 1869 | an extremely 1872 |
important means of transition: to give one
instance,—there instance,—there 1866 1869 | instance,— 1872 |
are are 1866 1869 | there are 1872 |
fish with gills or branchiæ that breathe the air dissolved in the water, at the same time that they breathe free air in their swimbladders, this latter organ
having a ductus pneumaticus for its supply and having a ductus pneumaticus for its supply and 1866 |
OMIT 1869 1872 |
being divided by highly vascular
partitions. partitions. 1866 |
partitions, and having a ductus pneumaticus for the supply of air. 1869 1872 |
To give another instance from the vegetable kingdom: plants climb by three distinct means, by spirally twining, by clasping a support with their sensitive tendrils, and by the emission of
aërial aërial 1866 1869 | aërial 1872 |
rootlets; these three means are usually found in distinct
genera or families, genera or families, 1866 |
groups, 1869 1872 |
but some few
plants plants 1866 1869 | species 1872 |
exhibit two of the means, or even all three, combined in the same individual. ↑1 blocks not present in 1866 1869 1872; present in 1859 1860 1861 | Two distinct organs sometimes perform simultaneously the same function in the same individual; to give one instance, there are fish with gills or branchiæ that breathe the air dissolved in the water, at the same time that they breathe free air in their swimbladders, this latter organ having a ductus pneumaticus for its supply, and being divided by highly vascular partitions.
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In these
cases,
one of the two organs
or means of performing the same function might or means of performing the same function might 1866 |
might with ease 1859 1860 |
might 1861 |
for performing the same function might 1869 |
might readily 1872 |
be modified and perfected so as to perform all the work
by itself,
being aided during the
process process 1859 1860 1861 1866 | progress 1869 1872 |
of modification by the other organ; and then this other organ might be modified for some other and quite distinct purpose, or be quite
obliterated. |