THE OCEAN FEEDING-GROUNDS 91 



figures. 1 Thus the mass of life distributed throughout 

 the ocean is in a condition of perpetual renewal, and 

 constitutes a perpetual reserve of matter and of energy. 



VI 



Now the time has come to consider the distribution of 

 plankton. We can distinguish two regions: the region 

 of neritic plankton and that of oceanic plankton. The 

 first corresponds with the in-shore and off-shore districts; 

 it therefore comprises the plankton of the waters of the 

 continental plateau. The second comprises the plankton 

 of the open sea. The former does not descend lower than 

 100 fathoms ; the latter may sink to the lowest depths. The 

 limit of the penetration of light that is, practically, from 

 100 to 130 fathoms marks the limit of penetration of vege- 

 table plankton, as there can be no vegetation without 

 light. Here is the result of a haul with a wide-mouthed 

 net made by the Prince of Monaco in latitude 45 30' N., 

 505' W. longitude, on the 6th September, at a depth of 

 800 fathoms, and above a depth of 2,500 fathoms : in- 

 numerable radiolaria, violet medusae, molluscs, innumer- 

 able little fish of the Syngnathus (pipe-fish) family, and 

 52 species of crustaceans. To sum up, we find plankton 

 everywhere, but there is a relation between the locality 

 and the nature of the plankton. This essential truth 

 must be emphasised. The microscopic shells at the 

 surface which fall to the bottom differ according to 

 the prevailing currents and temperatures. It therefore 

 follows that there are centres of planktonic production 

 whence a given flora and fauna overflow to a less or 

 greater distance. It seems to be proved that each system 

 of currents transports its particular flora and fauna. By 

 plankton-element we mean a methodical grouping of 



' See p. 22. 



