VII PELAGIC FORMS 203 



appearance of fine rain upon the surface of the sea. It occurs 

 in the open Atlantic and Mediterranean, hut comes into the 

 coasts during violent storms ; the ISTorwegian fishermen hail its 

 presence in the fjords as the sign of the approach of the summer 

 herring. 



It was Haeckel ^ who first clearly distinguished between 

 " neritic " plankton, the species of which have their centres of 

 distribution in shallow coastal waters and die out gradually as 

 the open ocean is approached, and " oceanic " plankton which 

 is habitually found in the open sea, and though it may invade 

 the coasts is not dependent on the sea-bottom in any way. It 

 appears that although these two kinds of plankton may get 

 mixed up by currents and storms, they are always recruited by 

 new generations from the neritic or oceanic stations proper to 

 each kind. 



Common oceanic species, found chiefly in the open Atlantic 

 and in the North Sea, are Anomalocera imttersoni, Calanus fin- 

 marchicus, Centropages typicus, Metridia lucens, OWiona plumifera, 

 etc. Common neritic species in the Channel and other coastal 

 waters are Centroyaucs hamatus, Euteipe acutifrons, Oithona nana, 

 Temora longicornis, etc. It was found by Gough ^ that although 

 the true oceanic species invade the Channel from the open 

 Atlantic to the west, they become rarer and rarer as they advance 

 up the Channel. Thus the plankton midway between the Lizard 

 and Ushant at all times of year is about 70 per cent, oceanic, 

 while at the line drawn from Portland to the Cap de la Hague it 

 is about 35 per cent. Seasonal changes in the salinity of the 

 Channel water, chielly due to the influx of oceanic water from 

 the Atlantic, as observed by Matthews,^ do not clearly influence 

 the distribution of oceanic and neritic forms. The influx of 

 highly saline water from the Atlantic was most marked during 

 the winter months up to February. From February to May the 

 highly saline water receded, and during the summer months at 

 the line drawn between Portland and the Cap de la Hague the 

 salinity was rather low. This was increased in November by a 

 patch of oceanic water being cut off from the main mass and 

 passing up Channel, and it is noteworthy that during this month 



' PlanktoHstudien, Jena, 1890. 



- "Report on the Plankton," Intcrnat. Inst. Marine Biol. 1903. 



=* Internaf. Inst. Mar. BioK 1903. 



