(715). Many of the smaller marine Annelids are luminous; their luminosity, however, is not a steady glow like that of the glow-worm or fire-fly, but a series of vivid scintillations (strongly resembling those produced by an electrical discharge through a tube spotted with tin-foil) that pass along a considerable number of segments, lasting for an instant only, but capable of being repeatedly excited by any irritation applied to the body of the animal. These scintillations may be observed even in separated segments if they be subjected to the irritation of a needlepoint or of gentle pressure; and it has been ascertained by M. de Quatrefages that they are given out by the muscular fibres in the act of contraction¶.

* Ann. des Sci. Nat. t. xxii. 1 Icones Physiologicse, pl. 28.

2 De Bopyro et Nereide, pl. 2. figs. 4 & 5. § Lehrbuch der vergleichenden Anatomie, p. 200.

║ Lehrbuch der vergleichenden Anatomie von Siebold und Stannius, p. 201. ¶ See his Memoirs on the Annelida of La Manche, in Ann. des Sci. Nat. ser. 2. t. xix. and ser. 3. t. xiv.