FOOT ON ANIMAL LUMINOSITY. 49 



once by replacing in it some of the Noctilucae which had been removed 

 from it by filtratioD. Infusoria, of the genus Peredinium, contribute 

 to the phosphorescence of the Baltic Sea. Some fresh-water Infusoria 

 are also possessed of luminous properties. Sir Philip Crarapton ob- 

 served phosphorescence in the water of Lough Bray, and the surface of 

 a piece of muslin through which some of the water of the lake had been 

 strained presented a luminous appearance.* The light emitted by 

 Noctiluca miliaris appears to be the combined result of a rapid succes- 

 sion of vivid scintillations, differing in this respect from the steady 

 glow of posthumous phosphorescence in fishes. No photogenic appa- 

 ratus, or special organ for the production of light, similar to that which 

 is observable in luminous insects, is discernible in the simple organisms 

 of the Infusoria ; every part of the structure seems to have the power 

 of emitting a nebulous light, resolvable with high magnifying powers 

 into an infinite number of sparks. There is no sensible development of 

 heat, no evidence of any secretion of a luminous mucus, nor does the 

 emission of light appear to be connected with combustion of any kind ;f 

 sulphuretted hydrogen passed into the water, or a few drops of ether 

 dropped upon it instantly destroys the luminosity of the Noctilucae. 

 Another cause of the phosphorescence of the sea is the luminosity of 

 various orders of the Hydrozoa and Actinizoa, especially of the order 

 Medusidae. According to Ehrenberg, the Arabians on the Red Sea 

 name the entire family of Medusae "Sea Candles" (Kandil el Bahr); 

 and Spallanzani observes that the luminous Medusae are called by the 

 same name in the Lipari Islands (Candelliere di mare). Dr. Macartney J 

 was inclined to attribute the principal portion of the phosphorescence 

 of the sea around our own islands to a species of Medusa of very small 

 size (M. scintillans), first described by himself, and which are frequently 

 present in these waters in great abundance. On one occasion he sepa- 

 rated a pint of these Medusae from a gallon of sea water by straining 

 through a cloth. He observed these Medusae to continue to emit light 

 when put under the receiver of an air pump, notwithstanding complete 

 exhaustion of air, and he satisfied himself that the light was by no means 

 of the nature of phosphorus, as it was often most strongly shown when 

 excluded from oxygen gas; when electrical shocks were transmitted 

 through a collection of them, they were excited, and shone with great bril- 

 Uslugj. Dr. Macartney's observations were communicated to the Royal 

 Society in 1810. Many of the fixed Hydrozoa are endowed with phospho- 

 rescent properties, several of our native Sertularidae glowing when irri- 

 tated with greenish light, like that of burning silver. In a foreign spe- 

 cies, Darwin § observed that the flashes of light always proceeded up 

 the branches, from the base towards the extremities, as often as he rubbed 

 any part of a branch. The Sea-pens exhibit a beautiful phosphores- 



* Sir H. Marsh, op. cit., p. 24. 



f Quatrefages, " An. de Sci. Nat.," 1850, 3d ser., t. xiv. p. 236. • 

 X " Observations upon Luminous Animals," Phil. Trans., 1810, p. 258. 

 § " Naturalist's Voyage round the World," p. 202. 



VOL. VI. H 



