THE TEEMING LIFE OF THE WATERS 



But this population fixed to the bottom is not really 

 very large; it covers the bottom only in places; it 

 penetrates a little way into the mud or sand, and goes 

 no farther. The population which floats in the water, 

 which allows itself to be carried along by the water 

 or else moves by its own power, is more varied. It 

 occupies the entire mass from the bottom, hundreds 

 and thousands of yards below, to the surface. It 



F IG- y. — One of the Wing-footed Molluscs, Venus's Shoe. The figure 

 shows the transparent shell in the shape of a shoe. The hollow 

 contains the animal, with the two outgrowths which enable it to 

 float. The shell usually measures about two inches in length. 



extends in breadth as well as in depth. Sometimes 

 spread out and scattered, almost lost in the vast volume 

 of its environment, elsewhere it is gathered in extensive, 

 closely packed shoals, in which millions of individuals, 

 as closely packed as the mussels on their rocks, fill 

 the waters of the surface for several yards in depth as 

 far as the eye can see. 



In certain localities, like Villefranche near Nice, 

 where currents, richly populated by these floating 

 creatures, often approach the shores from the open sea, 



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