THE PELAGIC FAUNA AND FLORA. 



199 



islands. The phosphorescence, in consequence, is far less bril- 

 liant than in the Gulf of Mexico, althousfh occasionally masses of 

 ctenophores (a species of Mnemiopsis) (Fig. 128), swimming at 

 different depths, produce a very striking illumination ; sudden 

 flashes of light appear, as if from gTeat balls of fire floating 

 a short distance below the surface. 

 The most surprising phosphorescent 

 phenomena were produced by a 

 smaU anneHd allied to SyUis which 

 we found in Petite Bale d'Arlet. 

 Just after dark, the bay was cov- 

 ered for a time with hundreds of 

 phosphorescent spots gHding slowly 

 about, when suddenly a number of 

 them began to move actively, per- 

 forming the most remarkable gy- 

 rations. Soon the whole bay was 

 traversed by brilliant phosphorescent 

 trains, made up of small particles of 

 light, which remained refulgent for 

 a while, so that the track, winding 

 swiftly in and out, backwards and forwards, could be distinctly 

 made out till the light became exliausted. After a period of 

 rest the process was repeated. Several deep-water species of 

 Gorgonia and Antipathes (especially Riisea) showed a bright 

 bluish phosphorescence when coming up in the trawl. An 

 ophiuran also, like one of the Mediterranean species men- 

 tioned by Panceri, was exceedingly phosphorescent, emitting 

 at the joints along the whole length of its arms a bright bluish- 

 green light. Among the deep-sea fishes certain parts, either 

 lateral organs or specialized parts of the head, are highly phos- 

 phorescent. 



It is interesting to note that Professor Forel, who has studied 

 the habits of the pelagic fauna of the large Swiss lakes, finds 

 that, like the marine pelagic fauna, the animals marked for 

 their transparency, especiaUy the Crustacea, sink to small depths 

 during the day and come up at night, to feed upon the pelagic 

 algse. 



Fig. 128. — Mnemiopsis Leidyi. 

 Somewhat reduced. 



