THE SWAN-MUSSEL, 39 



Occasionally they will wade a little way into shallow 

 water in search of the mussels, if none are exposed 

 on the bank, and it is amusing to watch them 

 hurriedly take flight from the surface of the water 

 as they now and then get suddenly out of their 

 depth. Their efforts, also, to land a heavy mussel, 

 and at the same time to save a ducking, are worth 

 noticing. 



Independently of its large size, the common swan- 

 mussel, Anodonta (PI. III., fig. 3), differs, as its 

 name implies, from the Unios in the absence of 

 teeth upon the hinge, although it would perhaps be 

 more correct to speak of these processes as rudi- 

 mentary only. Like the pearl-bearing mussels, this 

 species produces eggs, which it retains within its 

 shell, or, more correctly speaking, within its gills, 

 until they are hatched ; but the young are at first so 

 unlike the adult that, as they have been frequently 

 found adhering to the bodies of fishes, they have 

 been erroneously regarded as parasites. 



The large fleshy foot of these mussels enables 

 them to travel considerable distances, and " plough- 

 ing the deep " may be said to be literally part of 

 their occupation, as any one will admit who examines 



