250 LUMINOUS MOLLUSCA. 



probably not fanciful but real ; for the great Humboldt has 

 proved that the Salpae (Biphores of the French), as well as 

 the Pyrosomae, when preserved in a bottle, make the tem- 

 perature of the water rise nearly one centigrade degree. 

 The same naturalist, so remarkable for the extent and uni- 

 versality of his knowledge, tells us that the Pyrosoma atlan- 

 ticurn diffuses, " while swimming beneath the surface of the 

 sea, a light of a foot and a half in diameter. Only imagine 

 the superb spectacle which we enjoyed some days ago, when, 

 in the evening, from seven to eleven o'clock, a continuous 

 band of those living globes of fire passed near our vessel. 

 With the light which they diffused, we could distinguish, at 

 a depth of fifteen feet, the individuals of Thynnus, Pelamys, 

 and Sardon, which have followed us these several weeks, 

 notwithstanding the great celerity with which we have 

 sailed."* Mr. Thompson has given an interesting account 

 of the same species. It presents itself to the astonished voy- 

 ager, in the calm latitudes near to the line, under the appear- 

 ance of thick bars of metal of about half a foot in length, 

 ignited to whiteness, scattered over the surface of the ocean. 

 Some assume the luminous state, and continue so as long 

 as they remain in view ; while, in others, the luminosity 

 declines and disappears. " The greater number of these ap- 

 parently incandescent masses pass close to the sides of the 

 vessel, or follow in her wake : their phosphorescence being 

 called into activity by coming in contact with her prow or 

 bottom, as that of such as are more distant appears to be, by 

 the conflict of the waves." The light appears to pervade 

 the whole substance of the animal, and, " when examined 

 near at hand, varies in intensity and in shade, often exhibit- 

 ing a very beautiful phosphorescence of a bluish or greenish 

 tinge, like a pale sapphire or aquamarine, as it gradually 

 fades away. Agitation or friction renews it, as in other 

 luminous animals, as long as it continues to exhibit signs of 

 life ; but it is most vivid when the animal is first drawn up, 

 and at length can scarcely be called forth by the rudest 

 treatment. As we observed this interesting animal, with 

 Milbert's florid description at hand, I can aver that the red, 

 aurora, and orange colours did not present themselves to the 

 eyes of any of our numerous party, who were, nevertheless, 



and Hanley say, "Peculiar crustaceans make use of the cavity of the Salpa 

 as a dwelling-place and carriage ; and the number of minute phosphorescent 

 animals which lodge themselves within it is often so great as to mislead the 

 observer into the belief that it is the mollusk itself which gives out phos- 

 phorescent flashes." Brit. Mollusca, i. 47. 

 * Edinb. Phil. Journ. xii. 185. 



