THE PELAGIC FAUNA AND FLORA. 199 
islands. The phosphorescence, in consequence, is far less bril- 
liant than in the Gulf of Mexico, although 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 great balls of fire floating 
a short distance below the surface. 
The most surprising phosphorescent 
phenomena were produced by a 
small annelid allied to Syllis which 
we found in Petite Baie d’Arlet. 
Just after dark, the bay was cov- 
ered for a time with hundreds of 
phosphorescent spots gliding 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 Рів. 128. — Mnemiopsis Leidyi. 
Е Somewhat reduced. 
a while, so that the track, winding 
swiftly in and out, backwards and forwards, could be distinetly 
made out till the light became exhausted. 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, especially the erustacea, sink to small depths 
during the day and come up at night, to feed upon the pelagic 
algæ, 
