192 ^ THE PRODUCTIVITY OF THE SEA [PART II 



because the siliceous skeleton forms a relatively large part of 

 the mass of the organism. Peridinians, such as Ceratium or 

 Peridinium, are much more favourable, and a catch consisting 

 chiefly of these protozoa is not unlike, in its chemical composition, 

 that of a rye crop ; and Brandt places them in an intermediate 

 position between rye and good meadow hay. 



It is interesting to compare these three predominant planktonic 

 organisms with regard to the mass of dry organic substance 

 afforded by corresponding numbers of individuals. Thus : 



1 gram dry copepod substance corresponds to 675 millions of 

 the diatom Chaetocei^os ; and to 42 to 65 millions of peridinians ; 

 and to 300,000 to 500,000 copepods ; 



or, putting it in another way : — 



1 copepod contains as much dry substance as 135 peridinians, 

 or 1687 diatoms; and one peridinian contains as much dry 

 matter as 12 diatoms. 



The relative productivity of the sea and land. We see 

 then that the land and sea afford organic products which may 

 be compared with others in respect of their chemical composition 

 and suitability as human food. Fish flesh may be compared 

 directly with such land produce as beef, mutton and pork. The 

 marine shellfish products, such as molluscan and crustacean flesh, 

 differ notably from the flesh of farm animals but obviously belong 

 to the same category of produce. The plankton is comparable with 

 the land crops, so that a mixed catch of the former does not differ 

 greatly in composition from that of a crop of meadow hay, or from 

 ordinary pasture. In every way, the plankton is to be compared 

 with pasture ; not only in composition but in function, since the 

 former is indirectly or directly utilised as food by marine animals 

 which in their turn afford a flesh product to the fisherman ; while 

 pasture is, of course, utilised in just the same way by the animals 

 raised by the farmers. Land and sea then yield corresponding 

 products. Is it possible to compare the relative productivities 

 of the two regions ? 



There are unfortunately but slender data available for such 

 a comparison. Agriculture is a much more highly developed 



