Origin of Species Variorum

→ subsequently become modified and adapted 1861 1866 1869

subse- quently become modified and adapted 1859 1860

could, it is probable, become adapted without much difficulty 1872

→ are 1859 1860 1861 1866 1869

ova, as well as the adults, are 1872

→ sea-water, 1860 1861 1866 1869

sea water, as 1859

sea-water. 1872

→ remain to 1859 1860 1861 1866 1869

no doubt will 1872

→ a duck's feet 1861 1866

a duck's feet, which might represent those of a bird sleeping in a natural pond, 1859

a ducks feet, which might represent those of a bird sleeping in a natural pond, 1860

a ducks feet 1869

the feet of a duck 1872

→ would be sure to alight on a pool or rivulet, 1859 1860 1861 1866

OMIT 1869 1872

→ point. 1859 1860 1861 1866

point would be sure to alight on a pool or rivulet. 1869

point, would be sure to alight on a pool or rivulet. 1872

of the sea, and →subsequently become modified and adapted to the fresh waters of a distant land.

Some species of fresh-water shells have

very wide

ranges,

range,

and allied

species

species,

which, on

our

theory, are descended from a common

parent

parent,

and must have proceeded from a single source, prevail throughout the world. Their distribution at first perplexed me much, as their ova are not likely to be transported by

birds;

birds,

and

the

~~they~~

they

→are immediately killed by →sea-water,

are

~~as are~~

as are

~~the~~

the

~~adults.~~

adults.

I could not even understand how some naturalised species have

spread rapidly

rapidly spread

throughout the same country. But two facts, which I have observed— and

~~no doubt~~

no doubt

many others →remain to be

discovered—

observed—

throw some light on this subject. When

ducks

duck

suddenly

emerge

emerges

from a pond covered with duck-weed, I have twice seen these little plants adhering to

their

its

backs;

back;

and it has happened to me, in removing a little duck-weed from one aquarium to another, that I have

~~quite~~

quite

unintentionally stocked the one with fresh-water shells from the other. But another agency is perhaps more effectual: I suspended →a duck's feet in an aquarium, where many ova of fresh-water shells were hatching; and I found that numbers of the extremely minute and

just hatched

just-hatched

shells crawled on the feet, and clung to them so firmly that when taken out of the water they could not be jarred off, though at a somewhat more advanced age they would voluntarily drop off. These

just hatched

just-hatched

molluscs, though aquatic in their nature, survived on the

ducks

duck's

feet, in damp air, from twelve to

twenty-hours;

twenty hours;

and in this length of time a duck or heron might fly at least six or seven hundred miles, and →would be sure to alight on a pool or rivulet, if blown across

the sea

sea

to an oceanic

island,

island

or to any other distant →point. Sir Charles Lyell

~~also~~

also

informs me that a

Dytiscus

Dyticus

has been caught with an Ancylus (a fresh-water shell