192 BRITISH FISHERIES 



inspection. The real differences are physiological, 

 not morphological. A plant feeds in a different 

 manner from an animal. The latter must obtain 

 for its food the living or dead tissues of another 

 animal or plant ; the former can utilise material 

 which is not alive. The animal feeds on organised, 

 the plant on inorganic, materials. Now, since it 

 is only the plants which can convert inorganic 

 materials into a form suitable for assimilation by 

 animals, it follows necessarily that the animals are 

 in the long run ultimately dependent on the 

 plants. No matter how many forms of life may 

 be intercalated between the cod and the diatoms 

 or other plant-material on which the copepods 

 feed, or between the plaice and the diatoms on 

 which bivalve shell-fish feed, it is no less true that 

 these plant-forms are the ultimate food of both 

 cod and plaice. The plankton constitutes the 

 " meadows of the sea." How rich these 

 " meadows " are has been estimated by Hensen 

 and his colleague, Brandt. In March, one par- 

 ticular species of diatom alone (Chcetoceros] was 

 so abundant in the West Baltic that there were 

 457 m illions * n every cubic metre of sea-water ; 

 that is, every block of water which measured about 

 one-third of an inch along each side contained 

 about 457 diatoms. Next to the diatoms, the 

 group of micro-crustacea known as copepods are 

 most important. Every cubic metre of West 

 Baltic water was estimated to contain about 



