Origin of Species Variorum

→ cases. 1859 1860 1861 1866 1869

cases; of these, some of the most difficult to explain are presented by fish. 1872

↑ 8 blocks not present in 1859 1860 1861 1866 1869; present in 1872

It was formerly believed that the same fresh-water species never existed on two continents distant from each other. But Dr. Günther has lately shown that the Galaxias attenuatus inhabits Tasmania, New Zealand, the Falkland Islands, and the mainland of South America. This is a wonderful case, and probably indicates dispersal from an Antarctic centre during a former warm period. This case, however, is rendered in some degree less surprising by the species of this genus having the power of crossing by some unknown means considerable spaces of open ocean: thus there is one species common to New Zealand and to the Auckland Islands, though separated by a distance of about 230 miles. On the same continent fresh-water fish often range widely, and as if capriciously; for in two adjoining river-systems some of the species may be the same, and some wholly different. It is probable that they are occasionally transported by what may be called accidental means. Thus fishes still alive are not very rarely dropped at distant points by whirlwinds; and it is known that the ova retain their vitality for a considerable time after removal from the water. Their dispersal may, however, be mainly attributed to changes in the level of the land within the recent period, causing rivers to flow into each other.

→ recent period in the 1859 1860 1861 1866

OMIT 1869

→ having 1859 1860 1861 1866

within the recent period, having 1869

→ from 1859 1860 1861 1866 1869

are continuous, and which consequently must from 1872

→ parted river-systems and 1859 1860 1861 1866

OMIT 1869 1872

→ seems to 1859 1860 1861 1866

of the river-systems, seems to 1869

of the river-systems on the two sides, 1872

→ With respect to allied 1859 1860 1861 1866 1869

Some 1872

→ occurring at very distant points of the world, no doubt there are many cases which cannot at present be explained: but some fresh-water fish 1859 1860 1861 1866

occurring at very distant points of the world, no doubt there, are many cases which cannot at present be explained: but some fresh-water fish 1869

OMIT 1872

↑ 1 blocks not present in 1859 1860 1861 1866 1869; present in 1872

Moreover Dr. Günther has recently been led by several considerations to infer that with fishes the same forms have a long endurance.

→ In the second place, 1859 1860 1861 1866 1869

OMIT 1872

→ fishes confined exclusively 1859 1860 1861 1866

which all the members are confined exclusively 1869

which all the members are confined 1872

→ we may imagine that 1859 1860 1861 1866

OMIT 1869 1872

→ member of 1859 1860 1861 1866

species of 1869

species belonging to 1872

We can here consider only a few →cases. ↑ In regard to fish, I believe that the same species never occur in the fresh waters of distant continents. But on the same continent the species often range widely and almost capriciously; for two river-systems will have some fish in common and some different. A few facts seem to favour the possibility of their occasional transport by accidental means; like that of the live fish not rarely dropped by whirlwinds in India, and the vitality of their ova when removed from the water. But I am inclined to attribute the dispersal of fresh-water fish mainly to

~~slight~~

slight

changes

within

the →recent period in the level of the

land

land,

→having caused rivers to flow into each other. Instances, also, could be given of this having occurred during floods, without any change of level. We have evidence in the loess of the Rhine of considerable changes of level in the land within a very recent geological period, and when the surface was peopled by existing land and fresh-water shells. The wide difference of the fish on

the opposite

opposite

sides of

most

continuous

mountain-ranges, which →from an early period

~~must~~

must

have →parted river-systems and completely prevented

the

their

inosculation

inosculation,

→seems to

leads

lead

the

this

same conclusion. →With respect to allied fresh-water fish →occurring at very distant points of the world, no doubt there are many cases which cannot at present be explained: but some fresh-water fish belong to very ancient forms, and in such cases there will have been ample time for great geographical changes, and consequently time and means for much migration. ↑ →In the second place,

Salt-water

salt-water

fish can with care be slowly accustomed to live in fresh water; and, according to Valenciennes, there is hardly a single group of →fishes confined exclusively to fresh water, so that →we may imagine that a marine →member of a fresh-water group might travel far along the shores