Note 454 — Chapter XVI
Reading edition
"Die Polycladen," Fauna u. Flora des Golfes von Neapel, Monog. v., Leipzig, 1884, and "Beiträge zu einer Trophocœltheorie," Jen. Zeits., xxxviii., pp. 1-373, 1904 (which see for a modern account of theories of metamerism).