This condition may be protracted in the segmentation of the egg of certain Higher Animals, such as Peripatus (Vol. V. p. 20). It is clearly only a secondary and derived condition.
The usual antecedent of change in the condition of the egg is "fertilisation"—its conjugation with the sperm; but this is not invariable; and a transitory sojourn of certain marine eggs in a liquid containing other substances than sea-water may induce the egg on its return to its native habitat to segment and develop. This has been mistermed "Chemical fertilisation," discovered within the last six years by Jacques Loeb, and already the subject of an enormous literature.
See Hartog in Rep. Brit. Ass. 1896, p. 933, 1900, p. 786.
Commonly called "fertilisation," or "sexual union," inadequate and misleading terms.
For details see Hartog, "Some Problems of Reproduction," Quart. Journ. Micr. Sci. xxxiii. p. 1, xlvii. p. 583; and Ann. Biol. vol. iv. (1895) 1897; E. B. Wilson, Yves Delage, and Henneguy (references on p. [3], note); and for a singularly clear and full treatment of the processes in Protozoa, Arnold Lang, Lehrb. d. Vergl. Anat. 2nd ed. Lief. 2, "Protozoa," 1900.