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Show [CHAP. XII. G EOG RAP HI CAL DISTRIBUTION. 338 b bl accor dI' ng t o D r. great southern water-lily 1 (pro ) i;' a heron's stomach; Rooker the N elumbium uteu~ et analogy makes me although I do not kno~ th: fac 'ther pond and getting a believe that a.he:on flyinl~ 0r~~~bly reject from its stemhearty meal of fis~, .wouthe~eeds of the N elumbiu1n "?-nach a pellet conta1nm£ . ht be dropped by the bn·d digested ; ~r t~e see s ml~ the same way as fish are whilst feeding Its young, d known so~etii?-es tohbe dr~~~:al means of distribut~on, it In considering t ese s hen a ond or stream IS first should be re~embered th:t :Ising islet, it will be unoccuformed, for 1n~tance, 0~ ore g will have a good chance pied; and. a single se~ h th~·e will always ~e a struggle of succeeding. Al~ho. gd' . duals of the spemes, however for life between t ~ ID I VI ond yet as the nuinber of few, already occupying d an~tE tho~e on the land, the comkinds is slll:al1, compare bwil ss severe between aquatic petition will proba~~y 1 ;ec~es. consequently an intrudthan between terres ria sf< i ~ country would have a er from the waters o~ a ore g lace tha~ in the case of better ?hance of. seizin"* eo~:o~d, ~lso, remember th~t terrestnal colonists. fresh-water productions are lo'Y In some, perhaps many, d th t we have reason to beheve the scale of natur~, an h a o-e or become modified less that such low ben~g~ .c ::a this will give longer ti~e quickly than the hig h . ation of the same aquatic than. the average ~o; :o: f::~~~ the pr~bability of many spemes. W. e sh1u rl ranged as continuously as fresh-species having. orne y ran e over immense ar~as, water productions ever can g ~tinct in intermediate and having subsequ~~tl~.b:~~t~o~ of fresh-water plants regions. But the WI . e ls rl hether retaining the sar;ne and of the lower anima s, w di'fied I believe mam- . £ · some degree mo ' identical orm ohln . d dispersal of their seeds and eggs ly depends on t e Wl e . 11 b fresh-water birds, whwh by animals, more e(fi.Clht yan~ naturally travel from ~ne have large powers o .Ig ' ieee of water. Nature, hke to another and often dista~\[ her seeds from a bed of a a careful gardener' tgfu. a ~hem in another equally well particular nature, an ops fitted for them. · · OBAP. XII.] OCEANIC ISLANDS. 839 On the Inhabitants of Oceanic Islands.--We now come to the last o~ the three classes of facts, which I 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 ha~e all pr?ceeded 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, 'Yhich, if ~eg~timately followed out, would lead to the behef that Witl:nn the recent period all exis~ing island~ ha:e been nearly or quite joined to some conti~ent. This VIew . would r~move 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 co;nsider 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 : Alp~. 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 number, with those on an equal area at the' Cape of Good Hope or in Australia, we must, I think, admit that .somethi~g. 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 nu~ber~, and the comp~rison in some other respects is not qmte fair. We have ev1de1tce that the barren island of A~cension aboriginally possessed under half-a-dozen flowering plants; yet many have become naturalised on it, ~s th.ey h~ve on New Zealand and on every other oceanic Island whwh can be named. In St. Helena there is reason to believe that the naturalised plants and animals have nearly or quite exterminated many native productions. |
