CHAP. XI. LUMINOSITY OF THE SEA. 363 



(365.) The phosphorescence of the Mediterranean 

 sea has been highly admired by every naturalist who 

 has sailed along its " dark blue M waves. Spix, the 

 Brazilian traveller, had vessels filled with sea water in 

 this state, with which he made some very interesting 

 experiments. Whatever substance was wetted with 

 this water, shone ; and the vessels which held it, when 

 shaken, were found to be full of luminous particles. 

 When examined with a microscope, they were found 

 to be of different sizes, some roundish, some oblong, 

 and about the size of a poppy seed : each had, at one 

 end, a small navel-like opening, encircled with from 

 six to nine delicate filaments, which float within the 

 bladder, and with which the animal seems to attach 

 itself to other bodies. In the inside of these bladders 

 there were many other darker spots, of different sizes : 

 the larger ones might either be their spawn, or the 

 remains of smaller animals which they had swallowed. 

 These globular animalcule, which seem to be the 

 Noctiluca miliaris of Sayigny, or the Arethusa pelagica 

 of Peron, swim in greater or less numbers at night ; 

 and appear, to the naked eye, in sunshine, like little 

 drops of grease : they soon died when taken from the 

 sea, and fell to the bottom of the vessel which held them. 

 It is very singular, that when they came near to each 

 other, they seemed to be involuntarily attracted, and then 

 to form compact groups. A similar phenomenon has 

 been observed in the daytime ; but this is never wit- 

 nessed except when the sky is so very much clouded as 

 to darken the sea. Neither are they to be seen in salt 

 water taken up in the daytime ; so that they probably 

 sink to the bottom till night returns. Sometimes the sea 

 is covered with luminous balls, as large as a hazel nut, 

 when every wave, which strikes the ship, enlightens 

 all surrounding objects. There are, also, sometimes, 

 insulated luminous. bladders, like fiery balls, a foot in 

 diameter, which rise, singly, above the water; while the 

 striking of the waves together, at a distance from the 



