Many Nudibranchiate Mollusca undergo this change of habitat. See Garstang, Journal of the Marine Biological Assoc. n.s. i. No. 4, 1890, p. 447.
Chun, "Ctenophoren," Fauna u. Flora G. v. Neapel, Monogr. I. 1880, p. 180.
See Lang, "Polycladen," p. 607.
Lang, "Polycladen," Pl. 30, Fig. 8.
Kongl. Fysiograf. Sällskapets Handlingar, Bd. iv. Lund, 1892-93.