152 THE DISTRIBUTION OF THE PLANKTON [PART II 



Now if we study Cleve's chart of the distribution of these 

 plankton types in the North- Western Ocean during the summer 

 we will see that they are to be found over regions which have 

 very direct relationships to the distribution of the waters arising 

 out of the two great water circulations to which I have referred. 

 We will take them in the order mentioned. 



Tripos-Plankton (with several " neritic " types) is found in 

 the summer round the coast of Norway, in the North Sea, in the 

 Skagerak, to the south of Ireland, in the Bristol Channel and in 

 the Irish Sea. 



Styli-Plankton is found in the Atlantic between latitudes 

 40"" N. and 45° N., in the European Stream area, in the Bay of 

 Biscay and in the English Channel. 



Chaeto-Plankton is found also in the European Stream area 

 between the areas of Tricho- and >Sf^j/^i- Planktons. 



Desmo-Plankton is found in the west Atlantic south of 

 latitude 40°. 



Tricho-Plankton is present to the south and east of 

 Newfoundland, Greenland, Iceland, and in Davis Straits. 



Sira-Plankton is found in the sea near north Iceland, in 

 Davis Straits, off Labrador and Newfoundland. 



Now the reader must remember that the chart (which I 

 reproduce as Fig. 28) is only, as Cleve says, "a first essay in a 

 schematic plankton chart of the Atlantic, summer state." When 

 the reader considers the difficulty of obtaining simultaneous plank- 

 ton observations over such a wide area as the North Atlantic, and 

 further that such collections must be accompanied by observations 

 of the temperature and salinit}^ of the sea, he will see that any 

 single attempt at a schematic representation of the distribution of 

 the plankton over such a wide area must be imperfect and that 

 many such series of investigations must be made before we can be 

 sure that we have a normal sketch of the conditions of the area 

 investigated. 



Nevertheless we see in this chart a rough approximation of 

 the areas covered with plankton of distinctive types, with the 

 areas over which the sea water has common physical characters. 



