Molluscs 141 



the part of a bivalve to close on being 

 alarmed has been the undoing of many 

 a crow and water-rat, our native fresh- 

 water mussel being responsible for the 

 capture of many a small bird and 

 mammal. 



Many bivalves, by reason of their 

 limited powers of locomotion, are usually 

 condemned to lead sedentary lives. But 

 in some the development of the " foot ' 

 offers the possessor considerable change 

 of habitation. Cockles are notorious 

 nomads, ploughing through the sand at 

 the rate of a hundred yards per hour. 

 The bivalve foot can not only plough 

 the sand, but delve deep into it. The 

 more muscular the foot the deeper are 

 the digging capacities of the animal, and 

 the more specialised its breathing 

 apparatus. Bivalves penetrating several 

 feet beneath the surface have the siphon 

 pipes protected by a lengthy covering 

 and elongated to reach the surface. The 



