54 PHYSIOGNOMY OF PLANTS. 



the water, but the present state of our knowledge does not 

 permit us to receive this as a valid explanation. ( Joh. Reinh. 

 Forster's Bemerkungen auf seiner Eeise urn die Welt, 1783, 

 S. 57 ; Le Gentil, Yoyage dans les Mers de 1'Inde, 1779, 

 T. i. p. 685-698.) 



Perhaps there are few natural subjects of observation which 

 have been so long and so much debated as the luminosity of 

 the waters of the sea. What we know with certainty on the 

 subject may be reduced to the following simple facts. There 

 are several luminous animals which, when alive, give out 

 at pleasure a faint phosphoric light : this light is, in most 

 instances, rather bluish, as in Nereis noctiluca, Medusa 

 pelagica var. ft (Eorskal, Fauna JEgyptiaco-arabica, s. De- 

 scriptiones animalium quse in itinere oriental! observavit, 

 1775, p. 109), and in the Monophora noctiluca, dis- 

 covered in Baudin's expedition, (Bory de St.-Vincent, 

 Voyage dans les lies des 'Mers d'Afrique, 1804, T. i. 

 p f 107, pi. vi.) The luminous appearance of the sea is 

 due partly to living animals, such as are spoken of above, 

 and partly to organic fibres and membranes derived from the 

 destruction of these living torch-bearers. The first of these 

 causes is undoubtedly the most usual and most extensive. 

 In proportion as travellers engaged in the investigation of 

 natural phenomena have become more zealous in their 

 researches, and more experienced in the use of excellent 

 microscopes, we have seen in our zoological systems the 

 groups of Mollusca and Infusoria, which become luminous 

 either at pleasure or when excited by external stimulus, in- 

 crease more and more. 



The luminosity of the sea, so far as it is produced by 



