Origin of Species Variorum

Comparison with 1872

is small, compared with those on the land, the competition between them will probably be less severe .. than between terrestrial species; consequently an intruder from the waters of a foreign country, would have a better chance of seizing on a place, than in the case of terrestrial colonists. We should, also, remember that some, perhaps many, fresh-water productions are low in the scale of nature, and that we have reason to believe that such .. beings .. become modified more slowly than the high; and this will give .. time for the ... migration of .. aquatic species. We should not forget the probability of many fresh-water forms having formerly ranged .. continuously ... over immense areas, and then having become extinct at intermediate points. But the wide distribution of fresh-water plants and of the lower animals, whether retaining the same identical form or in some degree modified, apparently depends in main part on the wide dispersal of their seeds and eggs by animals, more especially by fresh-water birds, which have large powers of flight, and naturally travel from one to another and often distant piece of water. ↑

On the Inhabitants of Oceanic Islands .—

We now come to the last of the three classes of facts, which I have selected as presenting the greatest amount of difficulty with respect to distribution, on the view that only all the individuals both of the same ... species have migrated from some one area, but that allied species, although now inhabiting the most distant points, have proceeded from a single area,— the birthplace of their early progenitors. I have already given my reasons for disbelieving in continental extensions

is small in comparison with the number of species inhabiting an equal area of land, the competition will probably be less severe between aquatic than between terrestrial species; consequently an intruder from the waters of a foreign country will have a better chance of seizing on a new place, than in the case of terrestrial colonists. We should also remember that .. many fresh-water productions are low in the scale of nature, and .. we have reason to believe that .. low beings change or become modified less quickly than the high; and this will give a longer time than the average for the migration of the same aquatic species. We should not forget the probability of many species having formerly ranged as continuously as fresh-water productions ever can range, over immense areas, and having subsequently become extinct in intermediate regions. But the wide distribution of fresh-water plants and of the lower animals, whether retaining the same identical form or in some degree modified, I believe mainly depends on the wide dispersal of their seeds and eggs by animals, more especially by fresh-water birds, which have great powers of flight, and naturally travel from one ... piece of water to another. ↑

On the Inhabitants of Oceanic Islands .

We now come to the last of the three classes of facts, which I have selected as presenting the greatest amount of difficulty, if we accept the view that not only all the individuals .. of the same species, wherever found, have migrated from some one area, but that allied species, although now inhabiting the most distant points, have proceeded from a single area,— the birthplace of their early progenitor. I have already stated that I cannot honestly admit Forbess view on continental extensions,