Hyatt, Proc. Essex Institute (U.S.A.) (reprint from vols. iv., v. 1866-1868), p. 9.
Rare and Remarkable Animals of Scotland, ii. 1848, p. 93.
Trembley, Mém. Hist. Polypes, 1744; iii. Mém., p. 217. The same processes are described by Baker, Employment for the Microscope, new ed. 1785, p. 311.
Oka, J. Coll. Japan, iv. 1891, p. 90.
Hyatt, t. cit. p. 99.