ce 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- 
luses, 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 
