(Cambridge,
Mass., 1888), vol. i. p. 127, footnote.]

[Footnote 164: Even the extremely fine Mississippi mud is nowhere found
beyond a hundred miles from the mouths of the river in the Gulf of
Mexico (A. Agassiz, _Three Cruises of the Blake_, vol. i. p. 128).]

[Footnote 165: I have given a full summary of the evidence for the
permanence of oceanic and continental areas in my _Island Life_, chap.
vi.]

[Footnote 166: For a full account of the peculiarities of the Madagascar
fauna, see my _Island Life_, chap. xix.]

[Footnote 167: See _Island Life_, p. 446, and the whole of chaps. xxi.
xxii. More recent soundings have shown that the Map at p. 443, as well
as that of the Madagascar group at p. 387, are erroneous, the ocean
around Norfolk Island and in the Straits of Mozambique being more than
1000 fathoms deep. The general argument is, however, unaffected.]

[Footnote 168: For some details of these migrations, see the author's
_Geographical Distribution of Animals_, vol. i. p. 140; also Heilprin's
_Geographical and Geological Distribution of Animals_.]

[Footnote 169: For a full discussion of this question, see _Island
Life_, pp. 390-420.]

[Footnote 170: _Geographie Botanique_, p. 798.]

[Footnote 171: _Nature_, 1st April 1886.]

[Footnote 172: Report of the Brit. Assoc. Committee on Migration of
Birds during 1886.]

[Footnote 173: _Trans. Ent. Soc._, 1871, p. 184.]

[Footnote 174: _Nature_ (1875), vol. xii. pp. 279, 298.]

[Footnote 175: I am indebted to Professor R. Meldola of the Finsbury
Technical Institute, and Rev. T.D. Titmas of Charterhouse for furnishing
me with the weights required.]

[Footnote 176: See _Nature_, vol. vi. p. 164, for a summary of Kerner's
paper.]

[Footnote 177: It seems quite possible that the absence of pappus in
this case is a recent adaptation, and that it has been brought about by
causes similar to those which have reduced or aborted the wings of
insects in oceanic islands. For when a plant has once reached one of the
storm-swept islands of the southern ocean, the pappus will be injurious
for the same reason that the wings of insects are injurious, since it
will lead to the seeds being blown out to sea and destroyed. The seeds
which are heaviest and have least pappus will have the best chance of
falling on the ground and remaining there to germinate, and this process
of selection might rapidly lead to the entire disappearance of the
pappus.]

[Footnote 178: See _Island