[Footnote 41: It is probable that this shortening has resulted not
directly but indirectly, from the selection of individuals which were
noted for tenacity of hold; for the bull-dog's peculiarity in this
respect seems due to relative shortness of the upper jaw, giving the
underhung structure which, involving retreat of the nostrils, enables
the dog to continue breathing while holding.]
[Footnote 42: Though Mr. Darwin approved of this expression and
occasionally employed it, he did not adopt it for general use;
contending, very truly, that the expression Natural Selection is in some
cases more convenient. See _Animals and Plants under Domestication_
(first edition) Vol. i, p. 6; and _Origin of Species_ (sixth edition) p.
49.]
[Footnote 43: It is true that while not deliberately admitted by Mr.
Darwin, these effects are not denied by him. In his _Animals and Plants
under Domestication_ (vol. ii, 281), he refers to certain chapters in
the _Principles of Biology_, in which I have discussed this general
inter-action of the medium and the organism, and ascribed certain most
general traits to it. But though, by his expressions, he implies a
sympathetic attention to the argument, he does not in such way adopt the
conclusion as to assign to this factor any share in the genesis of
organic structures--much less that large share which I believe it has
had. I did not myself at that time, nor indeed until quite recently, see
how extensive and profound have been the influences on organization
which, as we shall presently see, are traceable to the early results of
this fundamental relation between organism and medium. I may add that it
is in an essay on "Transcendental Physiology," first published in 1857,
that the line of thought here followed out in its wider bearings, was
first entered upon.]
[Footnote 44: _Text-Book of Botany, &c._ by Julius Sachs. Translated by
A. W. Bennett and W. T. T. Dyer.]
[Footnote 45: _A Manual of the Infusoria_, by W. Saville Kent. Vol. i,
p. 232.]
[Footnote 46: _Ib._ Vol. i, p. 241.]
[Footnote 47: Kent, Vol. i, p. 56.]
[Footnote 48: _Ib._ Vol. i, p. 57.]
[Footnote 49: _The Elements of Comparative Anatomy_, by T. H. Huxley,
pp. 7-9.]
[Footnote 50: _A Treatise on Comparative Embryology_, by F. M. Balfour,
Vol. ii, chap. xiii.]
[Footnote 51: Sachs, p. 210.]
[Footnote 52: _Ibid._ pp. 83-4.]
[Footnote 53: _Ibid._ p. 185.]
[Footnote 54: _Ibid._ 80.]
[Footnote 55: Sachs, p. 83.]
[Footnote 56: _Ibid._ p. 147.]
[Footnote 57: _A Treatise on Comparative Embryology._ By Francis M.
Balfour, LL.D., F.R.S. Vol. ii, p. 343 (second edition).]
[Footnote 58: Balfour, l.c. Vol. ii, 400-1.]
[Footnote 59: Balfour, l.c. Vol. ii, p. 401.]
[Footnote 60: For a general delineation of the changes by which the
development is effected, see Balfour, l.c. Vol. ii, pp. 401-4.]
[Footnote 61: _See_ Balfour, Vol. i, 149 and Vol. ii, 343-4.]