114 < EMISSION OF LIGHT 



mous layer of shining phosphorus or molten lava. 

 These singular productions of nature are met with 

 between 19 and 20 of longitude east of Paris, 

 and 3 and 4 north latitude. 



The no less curious animals belonging to the 

 genus Salpa (fig. 13, Salpa cristata : 1, an iso- 

 lated individual; 2, five Salpae united as they 

 swim), also classed in the Tunicata, abound in the 



Fig. 13. 



Mediterranean and warmer parts of the ocean. 

 They are often phosphorescent. They also swim, 

 adhering together in vast numbers; their phos- 

 phorescence resembles the light of the moon on 

 the still waters, and they give rise to what is termed 

 by the French a mer de lait, or sea of milk. 



Sir Joseph Banks, in his voyage from Madeira 

 to Rio Janeiro, discovered the little crab Cancer 

 fulgens, a species said to be very phosphorescent. 

 In nearly the same latitude that this discovery 

 was made, Medusa pellucens was met with; its 

 phosphorescence is described as resembling a 

 flash of lightning. 



