[37]

Whitman, Journal of Morphology, vol. iv. 1890, p. 361.

[38]

A full account of Polyclad development is contained in Lang's "Polycladen," with references to the literature of the subject. Since the date of that work (1884) the embryology of Ctenophora has become better known, but, though the segmentation of the egg and early stages of development are very similar in both cases, the elaborate investigations of E. B. Wilson (Journ. Morphology, vol. vi. p. 361) show that the segmentation of Polychaet worms is again similar. The question of the affinities of the Polycladida is also discussed by Lang ("Polycladen" p. 642 et seq.). The work of the last decade has neither proved nor disproved his suggestion that the Ctenophores and Polyclads have been derived from common ancestors. On this subject the remarks made by Hatschek (Lehrbuch d. Zoologie, p. 319) are some of the weightiest that have appeared.

[39]

Hallez, Revue Biologique du Nord de la France, tom. ii. 1889-90.

[40]

Voigt, Zool. Anz. xv. p. 238.

[41]

Grube, Archiv f. Naturgeschichte, 38 Jahrg. Bd. i. 1872, p. 273.