OBSERVATIONS ON SOME MOLLUSCA AND ZOOPHYTES. 93 



thesis, we shall content ourselves with adding to the facts 

 already known some simple remarks, by means of which 

 more skilful observers may perhaps develop the cause of the 

 surprising power which those animals possess, which we are 

 now considering. 



We can no longer be in doubt as to the general causes of 

 the luminosity of the sea. Naturalists have shown that it is 

 produced by animalculae which multiply in its waters ; that 

 it belongs neither to the liquid, nor to electricity, still less 

 to putrefaction ; although in that state some mollusca, such 

 as the Salpae and Calmars, are susceptible of emitting some 

 light, although always of short duration. An active phos- 

 phorescence is essentially connected with life ; for animal- 

 culae and mollusca whose vital powers are weakened emit 

 scarcely any light, and that is extinguished when they cease to 

 exist. This luminosity is occasionally an inherent property of 

 the substance of some Medusae, Salpae, Beroes, &c, and these 

 animals are not able to strengthen or to weaken it. Others, 

 on the contrary, strange to say! enjo) this power, and can so 

 modify the light, that they spontaneously increase, diminish, 

 or extinguish it altogether, as we shall hereafter mention. 



Calm weather, heat, and a superabundance of electricity in 

 the atmosphere increase the intensity of the phosphorescence, 

 Night renders it more apparent, and agitation develops it. 

 All who have sailed between the tropics near to land, and in 

 tolerably shallow water, know what a brilliant train of light 

 the vessel leaves behind her. This beautiful light has exercised 

 the pen of more than one traveller ; and each, in describing 

 it according to the impression which it produced upon him, 

 has but too often embellished it still more by an exaggerated 

 description. However it may be, the development of phospho- 

 rescence by agitation is a truly wonderful circumstance. When 

 at rest, the waves do not make apparent any other light than 

 that of some large mollusca ; but when they are agitated, 

 every living molecule becomes luminous. And if at the same 

 time the active dolphins play around the ship, they seem to 

 resemble serpents of artificial lire under the water. But when 

 they respire the air with noise, the illusion increases, and we 

 seem to behold and hear the firing of a gun. 



No doubt the viscidity of the sea may be referred to this in- 

 calculable quantity of animalculae. The greater number, which 

 are invisible from their transparency, by the aid of phospho- 

 rescence become luminous points, which attach themselves to 

 anything that is plunged into the water. Hence probably has 

 arisen the idea that many living fishes were luminous : — it may 

 be so ; we do not deny it : yet we must consider them rare, 



