THE SEA SHORE 49 



and sea urchins all have special devices which enable them 

 to work their way through the sand or mud. 



Many fishes migrate long distances, usually because their 

 feeding and spawning grounds are far apart. There are 

 also migrations on the sea shore, though on a much smaller 

 scale. The movements of edible crabs have been studied, 

 and it has been found that they move from near the shore 

 into depths of twenty or thirty fathoms about the beginning 

 of autumn and remain there until February, when they 

 begin to return to the shore again. The eggs are laid in the 

 winter in deep water and remain attached to the body of 

 the female, finally hatching out during the summer in the 

 warmer water near the shore. Both temperature and food, 

 therefore, play a part in determining the yearly travels of the 

 crab and also of lobsters and prawns which, though we know 

 less of their habits, appear to migrate in a similar manner. 

 The shore fishes also move into deeper water in the winter, 

 while many of the bigger sea slugs, such as the Sea Hare 

 (Aplysia) and the large Plume-bearer {Oscanius) come on to 

 the shore during the summer specially for spawning. 

 Attention has already been drawn to the more localised 

 movements, apparently concerned with feeding only, of the 

 limpets, and this habit is also found in allied beasts. 



Spawning 



In such a difficult region as the sea shore, spawning 

 has to be carefully attended to if the race is to be continued. 

 Spring and early summer are the times usually chosen for 

 spawning, for the water is then teeming with microscopical 

 plant life, which forms ideal food for the newly-hatched 

 young. We may divide shore animals into three classes 

 according to their methods of reproduction ; those which 

 discharge their reproductive products freely into the sea 

 where they float helplessly until swimming organs are 



