360 Biology in America 



of equal weight, and a feather or sheet of paper falls more 

 slowly through the air than a tiny lead shot, which weighs 

 no more. Wonderfully varied and beautiful are the devices 

 with wliich Nature has furnished both plants and animals to 

 buoy them in the water. JNIany diatoms are provided with 

 long and exceedingly fine spines. The Radiolaria previously 

 mentioned also have numerous spine-like processes projecting 

 from their shells. Many molluscs have plate or wing-like 

 extensions of body or shell, secretions of slime, or air cham- 

 bers which aid in flotation. But perhaps the most beautiful 

 floating structures in the animal kingdom are found in the 

 Crustacea where antenna, feet and tail may be greatly length- 

 ened and finely branched, forming long, feathery processes 

 which, when extended, offer great resistance to the water and 

 serve admirably in keeping the animals afloat. 



AVhile many marine animals, and the same is true of fresh 

 water forms, are inactive swimmers, floating idly at the sur- 

 face of the sea ; or living a monotonous existence hidden away 

 in some obscure niche of coral reef, or groveling on the ocean 

 floor ; there are others, mariners bold, who fare forth in quest 

 of prey, making long journeys across the sea. Naturally the 

 chief of these are the whales and fishes, most of whom are 

 powerful swimmers, which follow their food from place to 

 place and whose presence can usually be predicted from the 

 presence of the latter. 



Experimental evidence of the migration of fishes has been 

 obtained in recent years by the International Council for 

 the Investigation of the Sea by marking fish, and then record- 

 ing so far as possible the number of marked fish caught. 

 This has also been practised on our Pacific salmon and a 

 similar method has been employed by American ornithologists 

 for studying the migration of birds. This has been employed 

 especially in studying the spawning migration of fish, and it 

 has been shown for example that the Iceland plaice mi- 

 grate hundreds of miles to and from their spawning 

 grounds. 



In 1888 and '98 two whales were taken off the coast of 

 northern Norway, each of which contained bomb lances of 

 American manufacture. These lances had evidently been 

 used by American whalers, which do not ordinarily cruise 

 off the Norwegian coasts, and the capture of whales contain- 

 ing these lances in Norway is probable evidence of ioug 

 journeys made by them. 



Even more interesting than the more or less sporadic move- 

 ments of aquatic animals in search of food are their periodic 

 journeys to and from their spawning grounds. The annual 

 run of the salmon, wliieh is described in another chapter. 



