IX THE SEA 347 



markable migrations, remain habitually near 

 the shore. Whales alone are specially modified 

 so as to make the wide ocean their home. Of 

 birds the greatest wanderer is the Albatross, 

 which has such powers of flight that it is said 

 even to sleep on the wing. 



Many Pelagic animals — Jelly-fishes, Mol- 

 luscs, Cuttle-fishes, Worms, Crustacea, and 

 some true fishes — are remarkable for having 

 become perfectly transparent ; their shells, 

 muscles, and even their blood have lost all 

 colour, or even undergone the further modifi- 

 cation of having become blue, often with 

 beautiful opalescent reflections. This obvi- 

 ously renders them less visible, and less liable 

 to danger. 



The sea-shore, wherever a firm hold can be 

 obtained, is covered with Sea-weeds, which 

 fall roughly into two main divisions, olive- 

 green and red, the latter colour having a special, 

 relation to light. These Sea-weeds afford 

 food and shelter to innumerable animals. 



The clear rocky pools left by the retiring 

 tide are richly clothed with green sea-weeds, 

 while against the sides are tufts of beautiful 



