VHOSPltOIiESClCNCn OF THE PBOlAS. 211 



tions, and enjoy abundance of water privilege. The 

 pholades, like other molluscs, exist in numerous colo- 

 nies, but all the members of this great family obey 

 tilt? word of command. Their mission is to go for 

 ever tmward, extending or enlarging their mine, and 

 leaving otf work only when they die. Thus employed, 

 their whole lives would be passed in darkness, if 

 nature had not provided every one of these little 

 miners with a lamp. The pholades are phospho- 

 rescent. 



This fact was remarked by Pliny, but the cause of 

 the phenomenon remained long unknown. Beaumur 

 observed that if he washed his hands after toucliing a 

 pholas, the water became phosj)horescent ; and at the 

 end of a certain time the phosphorescent matter fell 

 to the bottom of the vessel. We now know that the 

 phosphorescence is due to a liquid continually secreted 

 by the body of the animal. 



In contrast with these pioneers of the ocean, of these 

 slaves who precede and assist him in the destruction 

 of continents, there is a creature whose fate it is to 

 float incessantly in the water, at the mercy of the 

 most capricious winds and currents. We have already 

 seen (in the chapter on the Colour of the Ocean) that 

 the water holds in suspension a mass of microscopic 

 beings. It is to the existence of these creatures that 

 is due the yellowish milky, red, or olive-green tint 



