THE SHELL-FISH OF THE COAST. 83 
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 
longer 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 mass 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 
double tube or ‘siphon,’ through which water 
enters and leaves the interior of the shell. Not 
all bivalves have these siphons, but where they 
are well developed and retractile, a peculiar inflec- 
tion may be observed in the impressed line which 
c 
