PLAXIvTON. 



291 



the groves in Germany- are lighted up b^' thousands 

 of glow-worms (Lanipyi-fs iioclihica). Onh" the males of 

 these beetles tl\', dra^\•ing bright streaks through the air. 

 while the females, which are also luminous, remain on 

 the ground. 



The number of luminous inhabitants of the sea is 

 endless; almost e\-ery division of the Animal ^^''orld 

 contains luminous representati^■es. But only a few of 

 these creatures contribute to the nighth' illumination of 

 the surface of the sea. The rest live in the depths 

 below and shine in the perpetual darkness. The lighting 

 up of the surface of the sea is the result of the aggreg- 

 ation of countless numbers of lo\'\'l\' organisms. It is 

 the^" ^^ ho border each \\a\'e with a silver\ hem and 

 trace the ship's course as a shining furr<n\-. Most of 

 these organisms belong to the x\nimal \\ nrld, but man\' 

 minute plants are associated with them; these jiermeate 

 ihe sea and are kno\\-n as plaiikloii. This plankton 

 li\'es sus])ended in the upper la\"ers of the water, or at 

 night rises to the sm'lace. But the lier\' streaks ^\'hich 

 shoot through tlie water are emitted b\- more higliK' 

 organised creatures, generall\" those large bell -shaped 

 Medusae, ^^■hich the Arab so appropriateh' calls "Lant- 

 erns of the sea". 



There are light-emitting bacteria in the sea; these 

 are sometimes met with on land also. llre\- do not, 

 however, contribute to the illumination of tlie sea, 

 although thcA' are lound in all seas. The^" settle upon 

 other organisms which then begin to phosplioresce in 

 the clark ^^•ith a sil\■er^■ -white or bluish -green light. 



