THE FRESH WATERS 149 
THE WEB OF LIFE IN THE FRESH 
WATERS 
Nowhere do we find better examples of the 
web of life than in the fresh waters, meaning 
by the web of life the linkages between living 
creatures, binding them together. Here are 
some examples. 
The eggs of the common salt-water mussel are 
wafted out into the sea and develop into free- 
swimming larve, which eventually settle down; 
but the eggs of the fresh-water mussel are re- 
tained inside the shell and develop in a special 
brood-chamber, the cavity of the basket-work- 
like outer gill. They develop into tiny pinhead- 
like larve, called Glochidia, each with two 
valves toothed atthe margin. The eggs are pro- 
duced about midsummer in Britain, but the 
Glochidia are not allowed to escape till early 
in the following year. They are not allowed to 
escape unless a fish, such as a minnow, comes 
swimming slowly past. Then the mother- 
mussel allows some of her offspring to escape, 
and they come crowding out, like boys set free 
from school, clapping their valves in the water 
and exuding delicate gluey threads. Some of 
them are lucky enough to get attached to the 
