NATURE ADRIFT 



water rivers given on page 102 is one example. Many find their food or 

 their mates by smell and it is worth commenting on these two different 

 origins of the smell ; the one an extraneous source from the food, alive or 

 dead, and the other from its own species. The name 'pheromones' (from 

 the Greek pherein, to transfer) has been given to those substances secreted 

 to the outside by an individual which cause a reaction in another individual 

 of the same species. The best known pheromones are probably those liber- 

 ated into the air by female moths and which can attract the males from amaz- 

 ing distances. We know so little about their occurrence in the sea that there 

 is a whole field of research waiting to be done, but it is very probable that 

 the attraction between male and female plankton organisms is by phero- 

 mones. 



Lantern tish may be an exception. They have luminous organs, photo- 

 phores, arranged in specific patterns (Plate XXXI) which we find most 

 useful for identification. It has been suggested, but without any evidence 

 to prove it, that the lantern fishes also use them for the same purpose and 

 so find the right mates. Light from the photophores may also serve to 

 attract other curious animals and lure them close enough to be seen by the 

 owners. The luminous lure of the angler fish, dangling immediately above 

 a large gaping mouth, certainly serves such a purpose. 



Deep-sea fish are not the only luminous creatures in the plankton. 

 Many squids also have specific patterns of photophores (Plate XV). Look 

 over the side of the ship on a really dark night, especially towards the 

 summer in the higher latitudes. Every ripple in the water seems incandescent, 

 and every wave breaking on the beach has its shimmer of light. A general 

 greenish glow with no definable points of light is probably caused by 

 millions of dinoflagellates, each too small to be seen by the naked eye. 

 Minute pin-pricks of light are probably due to the larger dinoflagellate 

 Noctiltica or to small copepods. Bigger and more bluish flashes are caused 

 by larger copepods, euphausids, planktonic worms or small fish. A large 

 disc of pale light is probably a single medusa. Comb jellies are luminous 

 and the colonial Pyrosoiiia (p. 80) is a particularly brilliant form. One might 

 add to this list almost to the extent of asking if there are any planktonic 

 organisms which are not phosphorescent ! 



A last example of marine luminescence, not strictly planktonic but too 

 famihar to be overlooked, is that caused by bacteria in rotting fish. When 

 a fish is kept rather too long, it glows brilliantly in the dark. Such fish, 

 the trails they leave behind when moved and on fishermen's working 

 clothes have been the real origin of many a spooky story. 



We have yet a lot to learn about 'bioluminescence' as it is called. It can 

 usually be stimulated by disturbance in the water, but on some dark nights 



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