CH. IX] THE PRODUCTIVITY OF THE vSEA 191 



These analyses show that the plankton is to be compared with 

 the cereal and other crops : it represents the vegetation of the sea. 

 Marine animals such as fishes and shellfish are obviously to be 

 compared with the animals bred for human food. The dry 

 substance of the bodies of fishes contain more nitrogenous 

 substance and less fat than one finds in the bodies of farm 

 animals. Salmon and herring, as everyone knows, contain a 

 greater percentage of fat than does the flesh of most other edible 

 fishes, such as the cod and flounder. Crustacea, like the crab and 

 lobster, contain a large percentage of proteid and little fat, but a 

 small proportion of carbohydrate. On the other hand molluscs, like 

 the oyster and mussel, contain much about the same proportions 

 of proteid as does the flesh of lean farm animals, comparatively 

 little fat, and a considerable percentage of carbohydrate. 



The plankton is difficult to compare, as regards its chemical 

 composition, with land produce. It usually consists predominantly 

 of organisms like the diatoms and peridinians, and of copepods, or 

 larvae which resemble these in their composition. It contains the 

 "proximate principles," proteid, fat and carbohydrate, but the 

 relative proportions of these vary with the kind of organisms which 

 make up the mass of the plankton. A planktonic catch usually 

 contains a considerable percentage of ash, which comes from the 

 skeletons of the organisms — the siliceous shells of diatoms and 

 other limy or flinty skeletons; and in catches which consist 

 chiefly of diatoms, this siliceous ash is always considerable. A 

 plankton catch consisting chiefly of copepods does not correspond 

 in its chemical composition to that of any other animal. These 

 little Crustacea contain a relatively large percentage of proteid, 

 and a moderate amount of fat and carbohydrate. They resemble 

 more the composition of the oyster than that of any other common 

 animal. If they could be obtained in quantity the}^ might aflbrd 

 a highly desirable and nutritious food substance^. 



The diatoms, however, form but an indifferent '"' crop." The 

 proportion of proteid is small, and that of ash very high. This is 



1 They have indeed formed part of the menu of a yachting party. See Herdman 

 in Nature, July 23, 1891, p. 273 ; also Trans. Liverpool Biological Society, Vol. vi. 

 p. 78, 1892, for an account of such a culinary experiment, and for some interesting 

 suggestions as to the uses of copepoda as human food. 



