[24] Compare my Analytische Theorie der organischen Entwickelung, Leipzig, 1894, and my reviews in Ergebnisse der Anatomie und Entwickelungsgeschichte, vols. viii. xi. xiv., 1899–1905. A shorter review is given in Ergebnisse der Physiologie, vol. v., 1906. The full literature will be found in these reviews.
[25] If the plane of section passes near the equator of the germ, two whole larvae may be formed also, but in the majority of cases the “animal” half does not go beyond the blastula. The specific features of the organisation of the protoplasm come into account here. See also page [65], note [17].
[26] A change of the position of the cell is of course effected by each variation of the direction of the cut, which is purely a matter of chance.
[27] The reader will remember (see page [65], note [17]), that even the germ of Echinus is not quite equipotential along its main axis, but it is equipotential in the strictest sense around this axis. The germs of certain medusae seem to be equipotential in every respect, even in their cleavage stages.
[28] Journ. Exp. Zool. 1, 1904.
[29] Great caution must be taken in attributing any specific morphogenetic part to differently coloured or constructed materials, which may be observed in the egg-protoplasm in certain cases. They may play such a part, but in other cases they certainly do not (see Lyon, Arch. Entw. Mech. 23, 1907). The final decision always depends on experiment.
[30] It seems that these physical conditions also—besides the real specifications in the organisation of the egg—may be different before and after maturation or (in other cases) fertilisation. (See Driesch, Archiv f. Entwickelungsmechanik, 7, p. 98; and Brachet, ibid. 22, p. 325.)
[31] Studien über Protoplasmamechanik, Leipzig, 1886.
[32] Unters. üb. mikroskopische Schäume und das Protoplasma, Leipzig, 1892.
[33] Jena. Zeitschr. 26, 1892.