146 Canadian Record of Science. 



the valves resting on their edges. To maintain this 

 position it is necessary that the bivalve should be par- 

 tially or completely buried in the sand or^ mud of the 

 bottom on which it lives. Through this material it 

 slowly moves by means of a muscular projection of the 

 under surface of the body shaped somewhat like a 

 ploughshare, called the Foot. The Lomellibranchiata 

 are sometimes termed Pelecypoda, literally axe-footed 

 Mollusca, on account of the shape of the foot. The 

 exceptional character of the Oyster is at once seen 

 when we state the foot is entirely atrophied and the 

 animal lies on one side on the superfical layer of the 

 bottom. The valve on which it lies is differently 

 shaped from the other, being usually flat or slightly 

 convex whilst the upper valve may be slightly concave. 

 To a certain extent the edible character of the Oyster is 

 due to the absence of a foot, for this organ with its 

 tough muscles is often found to be a somewhat indiges- 

 tible morsel in the case of other Mollusca which are 

 used for food. 



However different in appearance, practically all 

 Lamellibranchiata have the same method of gaining 

 their food. They all depend for a livelihood on the 

 small organisms which swim or float in the sea and 

 which are swept into their gaping mouths by the 

 currents produced by the cilia which cover the gills and 

 certain folds near the mouth termed the palps, reed- 

 ing and breathing are, one may say, performed at the 

 same time, for the inrushing water brings also the 

 oxygen, without which no animal can live. 



It will, therefore, be seen that the Oyster is a 

 peculiarly helpless Mollusc, for if it be situated in a 

 place where the water is poor in food material, it is 

 unable to leave it and starves to death. But a far 

 greater danger is that of suffocation. If the water be 

 too muddy, the particles of silt swept in will clog the 

 interstices of the delicate gills; -and the deposition of 

 mud may soon bury the animal alive. In the case of 

 other bivalves, no such catastrophe can occur, for they 

 can move so that the hinder part of the shell through 

 which the current enters, always protrudes into clean 



