90 SEA FISHERIES 



varies firstly by reason of the evolution of the organisms 

 themselves ; also because large quantities of plankton 

 are eaten by marine animals ; these two causes incessantly 

 weigh one against the other, and maintain the quantity 

 of "living matter" scattered through the ocean at an 

 almost constant level at any one season of the year. An 

 infinitesimal crustacean, the Cetochilus, often forms 

 enormous shoals which give the water a reddish tinge 

 for many square miles together. The fishermen of the 

 Firth of Forth give the name of " maider " to swarms of 

 similar crustaceans. The Red Sea owes its red colour to 

 accumulations of reddish algae ; the Baltic and the Green- 

 land waters owe their greenish tinge to swarms of green 

 algae. At the beginning of the summer the Norwegian 

 sea turns brown on account of the arrival of the brown 

 spores of diatoms. In April and May whitebait, a mix- 

 ture of young sprats, herrings, and sardines, swarm in 

 the bay of the Seine and along the English estuaries. 

 In spring the poutina, a mixture of atherines, small 

 sardines, and aphyes, invades the inlets of the Ligurian 

 coast. Such instances might be multiplied indefinitely. 

 The colossal number of pelagic creatures is due to the 

 intensity of their powers of reproduction. The protozoa 

 multiply with a rapidity that defies calculation. The 

 process of reproduction is simple in the extreme ; it 

 usually consists in the division of one creature into two 

 identical creatures. Sometimes there are spores, 1 which 

 develop without the aid of fertilisation ; sometimes there 

 are eggs, which only develop after fertilisation. All the 

 marine invertebrates and the fish produce eggs ; and in 

 respect of these eggs I have already given significant 



1 Simple undifferentiated cells, which at a given moment detach 

 themselves from the adult and reproduce it by a process of 

 division. 



