[433] "Die Gastraea-Theorie, die phylogenetische Classification des Thierreichs und die Homologie der Keimblaetter." _Jenaische Zeitschrift_, viii., pp. 1-55, 1874. "Die Gastrula und die Eifurchung der Thiere," _ibid._, ix., pp. 402-508, 1875. "Die Physemarien, Gastraeaden der Gegenwart," and "Nachtraege zur Gastraea-Theorie," _ibid._, x., pp. 55-98, 1876. Republished in _Biologische Studien_, 2nd part, _Studien zur Gastraea-Theorie_, 270 pp., 14 pls., Jena, 1877. [434] See _Ann. Mag. Nat. Hist._ (4), xi., p. 253. [435] Term first introduced in _Die Kalkschwaemme_, p. 468, 1872. [436] "On the Primitive Cell-layers of the Embryo as the Basis of Genealogical Classification of Animals, and on the Origin of Vascular and Lymph Systems," _Ann. Mag. Nat. Hist._ (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.