40 
story or the oak tree 
ing out the waste that is left. You can tell it is pumping 
because it gets larger and smaller and larger and smaller. 
The ameba is not the only one-celled form. Every 
drop of sea water contains millions of such humble crea¬ 
tures; some of them swim along by means of tiny threads 
which extend out beyond their bodies like the legs of a 
centipede. They are sea-dust, they are diatom, and sea- 
dust and diatom serve as food for sea worms. Then 
the whelk eats the worms, the codfish eats the whelk, 
and you and I eat the codfish! It sounds like a game, 
and perhaps it is—Nature’s great and fierce and splendid 
game called the Struggle for Existence. Catch-as-catch- 
can! Aren’t you glad you are not an ameba ? 
You can readily see why cells are not all the same kind 
or the same shape. Your hand is not the same shape as 
your foot, because it has not the same work to do. If 
all the cells in your body were the same shape and did 
the same work, you would 
d be nothing but a glorified 
® ameba! No indeed, your 
(I) cells are of many, many 
V.) different shapes and 
forms. You have gland 
// cells, muscle cells, and 
y) nerve cells; cells for grow¬ 
ing, moving, and knowing; 
