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 addition 

 to, the animal's usual organs of locomotion. 

 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 



FIG. 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 antennae or feelers on its head to give 

 a kind of rowing stroke. It does this for 



