DRIFTING LIFE 125 



the greatest quantities of animal life. Such indeed is the case. 

 The abundance of that little creature, the Calanus, and of the 

 shrimp-like euphausiids, has already been dwelt upon and 

 they too are to be found chiefly in the regions outlined above. 



But, while the plankton is present in greatest quantities 

 in these northern waters, it is remarkable that compared 

 with the plankton of the warm and tropical regions the 

 numbers of different kinds of animals are extremely few. 

 The catches made in the northern waters can almost be 

 described as monotonous in composition, that is, although 

 they are so large, they will be made up of only comparatively 

 few species of animals. To the collector then the catches 

 made in warmer regions prove vastly more interesting on 

 account of the wealth of different species to be found there, 

 even though they be present only in small numbers. One 

 example is sufficient to show how marked this difference is. 

 Of roughly three hundred species of copepods, while eighty 

 per cent, are to be found in the warm regions, only five per 

 cent, are found in the cold northern region and only two 

 per cent, in the southern. This phenomenon holds good 

 for all the different groups of animals represented in the 

 plankton. 



Apart from the excessive abundance of drifting life in 

 the colder waters, it is to be noticed that everywhere the 

 coastal regions are considerably richer than the waters of 

 the open ocean. The central regions of the North and 

 South Atlantic oceans are the poorest in plankton life, that 

 is the areas lying a little north and^a little south of the 

 equator. Actually in equatorial regions the plankton is a 

 little richer. The deep blue Sargasso Sea, in the centre 

 of the North Atlantic, is probably as barren as any region 

 in the world. There are several factors that together are 

 responsible for the abundance or poverty of plankton life, 

 but of greatest importance is the presence or absence of 



