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Show 388 GEOGRAPHICAL D ISTRIBUTION. CHAP. XII. d th t when a pond or stream it should be reme~bere ~n a rising islet, it will be is first formed, for I~stalnce, d or egg will have a good . d d a sing e see unoccupie ; an . ~lth h there will always be a chance of suc~eeding. .._ th:~~dividuals of the species, struggle for hfe between . any pond yet as the however few, already occupying d ith ~hose on the f k' d . small compare w number o In s I~ . '.11 probably be less severe 1 d th competition WI . an ' e t. than between terrestrial speCies ; con-betweetnl aqauna ~Icn trud er f rom the ·waters of a foreign sequen y would have a better chance of sei~ing on a coun tryt,h . the case of terrestrial colo rusts. We place an In f h houid also remember that some, perhaps many, res d s . ' rod~ctions are low in the scale of nature, .an water p h to believe that such low bmngs that we ave reason h h' h. change or become modified less quickly than t ef l~h' d thi ·u:rill give longer time than the average or e an s H • • . ation of the same aquatic speCies. vV should not ~ ~~g:t the probability or" many species having .formed~ ra~ed as continuously as fresh-water :produ~wns :~; can range, over immense are~s, and ~aving ~u :~~:e"ride become extinct in intermediate regions. u th lower distribution of fresh-water plants and. ~f t' e 1 form animals, whether retaining the s~me I ~n IC~e ends . . me degree modified, I beheve mainly p l or In so . d d by animas, on the wide dispersal of theu see ~ an eg?s lar ·e more especially by fresh-water buds, whiCh have ~o f fl. ·ht and naturally travel from one . powers o Ig ' . Nature, hke another and often distant piece of wa te~. f a bed of a careful gardener, thus takes ~er s~e s ::r equally a particular nature, and drops t em In an well fitted for them. . r l ds _We now On the Inhabitants of Oceanw .LS an · h' h I come to the last of the three classes of facts, w IC CHAP. XII. OCEANIC ISLANDS. 389 have selected as presenting the greatest amount of difficulty, on the view that all the individuals both of the same and of allied species have descended from a single parent; and therefore have all proceeded from a common birthplace, notwithstanding that in the course of time they have come to inhabit distant points of the globe. I have already stated that I cannot honestly admit Forbes's view on continental extensions, which, if legitimately followed out, would lead to the belief that within the recent period all existing islands have been nearly or quite joined to some continent. This view would remove many difficulties, but it would not, I think, explain all the facts in regard to insular productions. In the following remarks I shall not confine myself to the mere question of dispersal; but shall consider some other facts, which bear on the truth of the two theories of independent creation and of descent with modification. The species of all kinds which inhabit oceanic islands are few in number compared with those on equal continental areas: Alph. de Candolle admits this for plants, and Wollaston for insects. If we look to the large size and varied stations of New Zealand, extending over 780 miles of latitude, and compare its flowering plants, only 750 in nu1nber, with those on an equal area at the Cape of Good Hope or in Australia, we must, I think, admit that something quite independently of any difference in physical conditions has caused so great a difference in number. Even the uniform county of Cambridge has 847 plants, and the little island of Anglesea 764, but a few ferns and a few introduced plants are included in these numbers, and the comparison in some other respects is not quite fair. We have evidence that the barren island of Ascension aboriginally possessed under half-a-dozen flowering |