Origin of Species Variorum

←Subtitle not present 1859 1860 1861 Fresh-water Productions . 1866 1869 1872

→ I well remember, when first collecting in the fresh waters of Brazil, 1859 1860 1861 1866 1869

When first collecting in the fresh waters of Brazil, I well remember 1872

→ this power in 1859 1860 1861 1866 1869

the wide ranging power of 1872

→ of ranging widely, though so unexpected, 1859 1860 1861 1866 1869

OMIT 1872

→ and 1859 1860 1861 1866 1869

within their own countries; and 1872

→ 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.

CHAPTER

XIII.

XII.

GEOGRAPHICAL DISTRIBUTION—

continued.

continued .

Distribution of fresh-water productions— On the inhabitants of oceanic islands— Absence of Batrachians and of terrestrial Mammals— On the relation of the inhabitants of islands to those of the nearest mainland— On colonisation from the nearest source with subsequent modification— Summary of the last and present

chapter.

chapters.

→

lakes and

river systems

river-systems

are separated from each other by barriers of land, it might have been thought that fresh-water productions would not have ranged widely within the same country,

and,

and

as the sea is apparently a still more

formidable

impassable

barrier, that they

would never

never would

have extended to distant countries. But the case is exactly the reverse. Not only have many fresh-water species, belonging to

~~quite~~

quite

different classes, an enormous range, but allied species prevail in a remarkable manner throughout the world. →I well remember, when first collecting in the fresh waters of Brazil, feeling much surprise at the similarity of the fresh-water insects, shells, &c., and at the dissimilarity of the surrounding terrestrial beings, compared with those of Britain.

But →this power in fresh-water productions →of ranging widely, though so unexpected, can, I think, in most cases be explained by their having become fitted, in a manner highly useful to them, for short and frequent migrations from pond to pond, or from stream to

stream

stream;

→and liability to wide dispersal would follow from this capacity as an almost necessary consequence. We can here consider only a few →cases. ↑ In regard to