150 THE HAUNTS OF LIFE 
skin of the minnow; the others perish. The 
Glochidia are somehow attuned to answer 
back to minnow, and if we have some in a 
soup-plate they become greatly excited if a lit- 
tle piece of dead minnow is dropped into their 
midst. In some North American fresh-water 
mussels it is to one kind of fish, and to that 
alone, that the larve respond. So subtly inter- 
laced are the threads of the web of life. But 
returning to our own rivers and ponds, we find 
that the Glochidia remain for a considerable 
time on their bearer, the minnow, burrowing 
a little way into the flesh, and undergoing a 
great change in the architecture of their body. 
When the great change or metamorphosis is 
accomplished, they drop off into the mud and 
start an independent life as young fresh-water 
mussels, often far from the place where they 
were born. We understand then that the fresh- 
water mussel cannot continue its race unless 
there is this strange linkage with a minnow. 
And just as the mussel is linked to a fish, so 
there is a fish which is linked to the mussel. 
For the Bitterling, Rhodeus amarus, which 
lives in some continental rivers, has a long 
egg-laying tube with which the eggs are ac- 
tually injected into the fresh-water mussel. 
