352 



LE PLANKTON 



minute quantities but which form the necessary base for the development of plant-life. In other parts of 

 the Océan, thèse substances will help to sustain the organic life as soon as they reach the sea, but this 

 will not be the case to such an extent in the ice-covered Polar Sea, where they will consequently accu- 

 mulate more or less without being used, as long as the water is covered by the ice. The low tempe- 

 rature will also act in the same direction, on the one hand and retarding the development of organic life, 

 and on the other hand perhaps favouring the absorption of ammonia. 



The changes in the amount of free oxygen and nitrogen (as gas), and free carbonic acid, contained 

 in the sea-water, is probably of little importance in this respect, as well as carbonic acid, to give the 

 necessary conditions for the sustenance of organic life ; but some etfect may nevertheless be produced by 

 the fact that the polar surface-water, on account of its low température, has a great capacity for absorbing 

 oxygen (and carbonic acid ?) from the atmosphère ; and as there is little organic life to use it, the water 

 of the polar surface-current becomes gradually saturated with oxygen, and when somewhat heated in more 

 Southern latitudes, becomes supersaturated. It seems not improbable that this latter circumstance may 

 also hâve some stimulating effect upon organic life. 



When the polar waters, with thèse gradually accumulated favourable conditions for organic life, are 

 carried southward by the polar current towards 'ower latitudes, the ice-covering is gradually removed by mel- 

 ting ; the light obtains access to the water-surface, and the formation of the chlorophyl becomes possible ; 

 and simultaneously the température of the water is somewhat increased, which greatly facilitâtes the assi- 

 milation of nourishing substances. The resuit of this sudden change of conditions must necessarily be a 

 sudden and active flourishing of the vegetable, as well as the animal, plankton-life in ail régions where 

 the waters of polar currents carrying ice meet the warmer waters from the Atlantic (i). 



LES COPEPODES DE SURFACE 



Parmi le phytoplankton de la surface, vit en abondance l'un des Copépodes les 

 plus caractéristiques, Calanus hyperboreus Krôyer. 



Cette forme arctique est l'une des plus grandes que l'on connaisse dans son 

 ordre, et c'est, pour autant que nous sachions, le plus grand de tous les Copépodes 

 de surface. Il atteint la taille considérable de g millimètres et n'est guère dépassé que 

 par quelques formes abyssales, soit des mers polaires, soit des autres océans. 



Dans toute la région parcourue par la Belgica, Calanus hyperboreus est incon- 

 testablement la forme de surface prédominante et la plus typique. En certains points, 

 comme, par exemple, à la station 22, elle peut se trouver en quantités réellement 

 colossales. 



Le naturaliste du bord n'a pas observé que cette forme donnât lieu à des 

 phénomènes spéciaux de coloration de la mer. Mais, nous sommes cependant persuadés 



(ij MiDDENDORF has already suggested that the abondance of life, fish, etc., on the Finmark and Murman coasts may in 

 some way be due to the meeting « der Auslàufer des Golfstroms mit den nordischen Gewassern ». Pelermann's MUtcilungcn, 1871, p. 32. 



