NUTRITION AND METHODS OF FEEDING 199 



of the fixed plants in the food-economy of the sea-shore is 

 mainly indirect. They are little utilised in the living state 

 by animals, but they are useful in intercepting floating food 

 organisms for the benefit of creeping forms, such as Littorinas, 

 and when reduced to detritus they provide a living for a 

 host of creatures living in the substratum. Still another 

 source of food income to shore- dwelling forms is the quantity 

 of debris (jetsam) washed up on the shore, mainly after 

 storms. Much of this, however, is permanently deposited 

 only at the highest point reached by spring tides and is thus 

 out of reach of strictly tidal species. It is, however, greatly 

 utilised by amphipods, insects, and even birds. Methods 

 of obtaining food on the shore are extraordinarily varied 

 and interesting ; they range from simple non-selective 

 current-feeding to the highly specialised procedure employed 

 by, say, a starfish or an octopus. 



