THE SCHOOL OF THE SHORE 35 
weeds on which some animals browse, such as 
the Pellucid Limpet (Helcion pellucidum), 
well known for its beautiful blue-marked 
shell. Some animals that look as if they were 
eating the seaweed are feeding on microscopic 
plants on the surface of the fronds. Along 
with the seaweeds we must take the sea-grass, 
Zostera, a flowering plant very abundant in 
some shore waters. (2) There is, secondly, the 
result of the breaking down of seaweeds and 
sea-grass, the vegetable débris, the plant-dust. 
(3) There is, thirdly, the multitude of minute 
free-swimming and free-floating plants, such 
as Diatoms and Desmids. These are exceed- 
ingly abundant in near-shore waters, and get 
swept out to form Open-Sea Plankton. The 
shore-waters serve as a nursery for the Open 
Sea abundance of minute plants. (4) There are 
the minute free-swimming animals, some of 
which are hardly distinguishable from plants. 
(5) There is the material, both animal and 
vegetable, brought down from inland by rivers 
and streams, sometimes helped by the wind. 
We are not including the mineral matter 
brought down which serves to feed the shore 
plants. (6) There isthe jetsam brought in from 
the sea, for the receding tide sometimes leaves 
