THE OPEN SEA 95 
seas that the fishermen call it “whale- 
food.” 
Sometimes the special device for keeping 
afloat is just some transformation of, or addi- 
tion to, the animal’s usual organs of locomo- 
tion. Many of the tiny crustaceans, known as 
copepods or “water fleas,” have on the jointed 
legs that they possess, in common with their 
larger relatives—lobsters, shrimps, and the 
like—thin projecting spines, each bearing 
smaller spines, all so delicate and so much 
Fic. 8—AN OPEN-SEA “ WATER FLEA.” 
Showing Delicate Processes which make Flotation easy. 
interlaced that the whole structure has the 
appearance of a feather. But that is not 
enough to keep the copepod afloat; it uses 
the long antennz or feelers on its head to give 
a kind of rowing stroke. It does this for 
