50 NATURAL HISTORY SOCIETY OF DUBLIN. 



cence, which, as Forbes observed, when excited by shock, sparkles 

 onwards from the portion struck in an upward or distal direction, still, 

 however, continuing to be emitted from the point of prime contact. Of 

 one of this group (Renilla) Agassiz remarks that " it shines at night 

 with a golden-green light of a most wonderful softness ; when excited, 

 it flashes up more intensely, and when suddenly immersed into alcohol 

 throws out the most brilliant light." Several of the Ctenophora are 

 phosphorescent. Specially distinguished for its luminosity is the Cestum 

 veneris of the Mediterranean Sea, which has the form of a band of 

 more than five feet long and two inches broad, gleaming at night like a 

 ribbon of flame as it moves beneath the surface of the water. Various 

 genera of the family Beroidse are also possessed of luminous properties. 

 Among the marine Mollusca are found some of the most splendid instances 

 of luminosity. The Pyrosoma, or Fire-body, is one of them ; it is one 

 of the compound ascidians, and forms a cylinder six or seven inches in 

 length, open at one end, at the other closed, and bluntly rounded off. 

 Mr. F. D Bennett* observed that when a Pyrosoma was taken into the 

 hand out of a bucket of sea-water, the whole mass became instantly 

 illuminated by myriads of bright dots, much resembling in hue the 

 points on the elytra of a diamond beetle (Curculio imperialis). The 

 Pyrosoma, enveloped throughout its whole extent in a flame of bright 

 phosphorescence, shed sufficient light to render objects distinctly 

 visible in every part of an otherwise dark room. The light appeared 

 to be chiefly emitted from small specks of a brown or red colour, 

 embedded in the parenchymatous structure of the body, and inter- 

 mingled with the prominent rigid and pearly tubercules which stud 

 the surface of the mass. No light was emitted after the death of the 

 animal ; no luminous matter was communicated from the surface of 

 the Pyrosoma to any fluid or solid in contact with it, and the brown 

 specks did not emit any light after their removal from the body. 

 Friction at one point of the Pyrosoma induces the light at that point, 

 and from thence the phosphorescence spreads over the whole mass, 

 while the creature is quite freshly taken ; afterwards the illumination 

 arising from friction is only local, f The various forms of Salpa, 

 another ascidian Mollusk of gelatinous consistence, possesses luminous 

 powers. One of the Pteropodous Molluscs (Cleodora cuspidata) emits 

 a speck of delicate blue light, which shines through the apex of its 

 extremely thin and glossy shell. 



Two principal kinds of phosphorescence of the sea have been 

 observed — one in which the surface appears studded with scintillations 

 of a most vivid description, upon any agitation of the water ; a heavy 

 tropical shower, for example, is said to produce a gorgeous effect at 

 night upon the sea, when it is in this condition. This kind of phos- 

 phorescence is assigned by Mr. Bennett to the presence of the luminous 



* "Proc. Zool. Soc. Lond.," 1833, Pt. 1, p. 

 t Huxley, " Phil. Trans.," 1851, p. 580. 



