94 BOYS AND GIRLS IN BIOLOGY. 



digs a hole with his foot, which he uses as a drill, or 

 spade, and buries himself in the soft, warm mud, and 

 enjoys himself immensely. I suppose this is what is 

 meant by being " as happy as a clam." The clam is 

 one of the mussel's cousins. He has an ingenious way 



Fig. 92. 

 Left Half of Shell. 



'Mantle, partly 

 lifted up. 



Part of Foot. Gill. 



of making the hole in the mud large enough to hold 

 his shell. The foot is much smaller than the end of 

 the shell ; so he increases the size by filling his foot 

 with water while he is digging. But the oddest thing 

 of all about the foot is, that the ears lie in it. We 

 thought it very odd to see the little blood-animal — the 

 amceba — eat with its foot. Imagine you stretching out 



