STIIZOPOD.E. 39 



is variable and is stronger in the systole than in the 

 tUastole. Sometimes it continues for a quarter of an hour, 

 half an hour, or more ; bat at other times it suddenly 

 becomes extinguished, and does not re-appear till after a 

 considerable interval. These luminous medusa are called 

 Bromi at Messina — at the Lipari islands candellieri di mare.''' 

 (Travels, vol. IV. p. 229.) 



(C.) A third kind of luminosity, is peculiar to gulfs, 

 bays, shores and probably to parts of the ocean where the 

 bottom is at no great distance, in all the warmer regions 

 of the globe 5 here the luminosity is so predominant that 

 the slightest agitation of the waves, the passage offish, the 

 movement of the oars, or the way of a ship, produces a 

 diffused pale phosphorescence, and under some of its modi- 

 fications, resembles a sea of milk, or rather of some metal 

 in a state of igneous liquefaction. 



Passing for the moment some less common and peculiar 

 kinds of luminosity, it may be observed, that all the various 

 foregoing appearances, so interesting and often alarming 

 to those who travel by sea, have been ascribed at difi*erent 

 periods and by different individuals to a variety of causes, 

 viz. a, the absorbed light of the sun, disengaged by the friction 

 of the waves ; h, electricity, excited by the same means ; 

 c, phosphoric matter diffused through its mass ; rf, lastly, to 

 luminous marine animals. The investigations of the practi- 

 cal Naturalist have tended to set aside all these, with the 

 exception of the last, which would appear to be the sole 

 cause of this curious phenomenon, in all the modifications 

 above stated, as well as in every other instance : the first 

 and third kinds (A& C.) being attributable to minute crus- 

 taceous animals, the smaller medusae and mollusca;, and per- 

 haps some annelides, modified in degree, by the animalcules 

 being more or less scattered, and the prevalence of parti- 

 cular species : the second kind (B.) as already explained, 

 appears to be the production of medusae of a larger size, of 

 which as yet, but two species have been observed to be 



