r.)l;;] on Life in the Great Oceans 627 



many of them brilliantly phosphorescent ; the cell-walls are composed 

 of cellnlose or allied substance readily solul)le in sea-water, conse- 

 quently the remains of these organisms are never detected in marine 

 deposits. Among the flagellates of the open ocean Fyrocystis is 

 well known from the intensity of its phosphorescent light. 



The calcareous flagellates (Coccolithophoridas) have the cell- wall 

 strengthened by calcareous shields, sometimes with a central spine. 

 These shields (coccoliths and rhabdoliths) were known from the geo- 

 logical strata and from recent marine deposits long before the living 

 organisms (coccospheres and rhabdospheres) were discovered in the 

 surface waters of the ocean. 



The brown algae include the Xanthellge or " yellow cells " found 

 living in symbiosis with radiolaria and other invertebrates, evidently 

 to the mutual advantage of the plant and the animal. Among the 

 Ph£eodaria, a group of radiolarians inhabiting the deep sea, the 

 place of the yellow cells in the other radiolaria is apparently taken 

 by the ph^odellEe, dark-coloured cells, which may possibly be a lower 

 form of algal life than the yellow cells, and capable of evolving 

 oxygen under the influence of the phosphorescence of deep-sea 

 animals. 



Of the blue-green alga?, the best known is Trichodesmium, which 

 sometimes occurs in such abundance at the surface as to form a 

 scum of great extent, called by sailors " whales' spawn." The green 

 colour so conspicuous in the vegetation on land is found in the sea 

 apparently only in one form — the green alga Halosplurra. 



Bacteria are the most numerous and most widely distributed of 

 living plants, being found everywhere in earth, air and water, and as 

 parasites in plants and animals. With a few possible exceptions they 

 cannot live without carbonaceous and nitrogenous organic matters. 

 They are present everywhere in the ocean. It may be said that it is 

 the fate of all living substances to become sooner or later, directly or 

 indirectly, food for bacteria. Life, as a whole, could not continue 

 without bacteria. They do not originate life, but supply life with 

 the necessary material. One group is said to be practically indepen- 

 dent of organic compounds, being able, without chlorophyll and sun- 

 light, to appropriate the carbon dioxide from the atmosphere, and to 

 store up free nitrogen, thus giving some indication of how the first 

 forms of life to appear on the earth obtained their nourishment. 

 Phosphorescent bacteria are limited to ocean water, for they have 

 never been observed in fresh water ; indeed, no phosphorescent 

 organisms of any kind are known from fresh water, though the power 

 of emitting phosphorescent light is widely distrilrated in nearly all 

 groups of marine organisms. 



Turning now to the animal life in the ocean, it may be stated 

 that most marine animals are cold-blooded, the temperature of their 

 circulating fluid depending upon that of the sea-water in which they 

 live, the marine mammals (whales and seals) being the only repre- 



