VII PELAGIC FORMS 203 
appearance of fine ram upon the surface of the sea. It occurs 
in the open Atlantic and Mediterranean, but comes into the 
coasts during violent storms; the Norwegian 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 cn 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 pattersoni, Calanus fin- 
marchicus, Centropages typicus, Metridia lucens, Oithona plumifera, 
etc. Common neritic species in the Channel and other coastal 
waters are Centropages hamatus, Euterpe 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, chiefly 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 
! Planktonstudien, Jena, 1890. 
~ “Report on the Plankton,” Internat. Inst. Marine Biol. 1903. 
° Internat. Inst. Mar. Biol. 1903. 
