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 Iarva3 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. 



