THE SHELL-FISH OF THE COAST. 33 



will of the animal, operated in the closing of the 

 shell. It is the action of these ' adductor' muscles 

 pulling together which renders the opening of clams 

 such a hopeless and discouraging task to the un- 

 initiated. But traverse the adductors with a knife- 

 blade, and the shell immediately opens. And so, 

 on the death of the animal, when the adductors no 

 lo!iger possess vitality, the valves of the shell are 

 pulled apart by the elastic ligament, which always 

 suffers compression in the closed condition of the 

 shell. This accounts for the apparent anomaly that 

 dead shells are almost invariably open. 



If a living clam be carefully opened, it will be 

 found that a delicate membrane lines the shell on 

 each side, reaching almost to the free edge of the 

 shell ; this is the so-called ' mantle' Immediately 

 following the mantle we meet on either side with 

 a pair of membranous, leaf-like organs, the gills, 

 and between the gills again, occupying the cen- 

 tre, is the tough, fleshy naass which constitutes the 

 ' body' and ' foot' of the animal, the part which is 

 so generously partaken of by all lovers of the 

 shell-fish. Into this fleshy mass the aperture of 

 the mouth opens, and in it is contained the greater 

 part of the alimentary tract. At the back of the 

 animal the mantle-margins are united to one an- 

 other, and the mantle is itself drawn out into a 

 doable tube or ' siphon,' through which water 

 enters and leaves the interior of the shell. Not 

 all bivalves have these siphons, but where thpy 

 are well developed and retractile, a peculiar inflec- 

 tion may be observed in th^ impressed line ^hich 



