._ (4), xi., pp. 321-38, 1873.

[437] First distinguished in _Die Kalkschwaemme_, i., p.
465.

[438] Even in the 'seventies it was still believed by many
that the egg-nucleus disappeared on fertilisation. The
true nature of the process was not fully made out till
1875, when O. Hertwig observed the fusion of egg- and
sperm-nuclei in _Toxopneustes (Morph. Jahrb._, i.,
1876).

[439] _Studien z. Gastraea-Theorie_, p. 214, 1877. These
forms were known even in 1870 (Carter, _Ann. Mag. Nat.
Hist._ (4), vi., pp. 346-7), to be Foraminifera. The
figures of supposed collar-cells, etc., do credit to
Haeckel's imagination.

[440] _History of Creation_, Eng. Trans., ii., pp. 278 ff.

[441] _Systematische Phylogenie_, iii., p. 41, Berlin,
1895.

[442] "Notes on the Embryology and Classification of the
Animal Kingdom," _Q.J.M.S._ (n.s.), xvii., pp. 399-454,
1877.

[443] It was "part of the non-historic mechanism of
growth" (_loc. cit._, p. 418).

[444] _Treatise on Comparative Embryology_, ii., chap.
xiii., 1881. For a modern discussion of this problem,
see Hubrecht, _Q.J.M.S._, xlix., 1906.

[445] See Balfour, _loc. cit._, Chapter xiii.

[446] _A Treatise on Zoology_, Pt. ii., 1900. Introduction
by Sir E. Ray Lankester.

[447] _Studien zur Blaettertheorie_, Jena, 1879-80. "Die
Coelomtheorie, Versuch einer Erklaerung des mittleren
Keimblattes," _Jenaische Zeitschrift_, xv., pp. 1-150,
1882.

[448] For an historical account of this work, see
Lankester, _loc. cit._, pp. 21-37.

[449] _Proc. Roy. Soc._, 1883, and _Q.J.M.S._, xxiii.,
1883.

[450] "Origin of Metameric Segmentation," _Q.J.M.S._,
xxiv., pp. 43-82 1884.

[451] See further the same author's article "Embryology"
in the _Ency. Brit._, vol. xi., 11th ed., Cambridge,
1910.

[452] _Arch. f. mikr. Anat._, xiii., pp. 181-204, 1877.

[453] "Der Bau von Gunda segmentata," _Mitth. Zool. Stat.
Neap._, iii., pp. 187-250, 1882.

[454] "Die Polycladen," _Fauna u. Flora des Golfes von
Neapel_, Monog. v., Leipzig, 1884, and "Beitraege zu
einer Trophocoeltheorie," _Jen. Zeits._, xxxviii., pp.
1-373, 1904 (which see for a modern account of theories
of metamerism).

[455] "Die Abstammung der Anneliden u. Chordaten," _ Jen.
Zeits._, xxxix., pp. 151-76, 1905. "The Gastru