NOTES ON THE OYSTERCATCHER. 211 
morsel is prevented by pressure of the mandibles and the 
reverted cusps on the palate. 
When entrance has been gained through the middle part of a 
border, one end is cleared out first and then the other, the 
Mussel, if detached, being turned round by the Oystercatcher, 
and, if not, the Oystercatcher, after emptying the end farthest 
from itself, walks round to the opposite pole and clears out the 
other. When the chief part of the mollusc has been removed 
there remains material adhering to the inner surface of the 
valves, chiefly the mantle. ‘To remove this material the bill is 
employed like a pair of scissors. It is laid flatly on the inner 
surface of a valve near one end, and as it is pushed forward it 
snips away the adherent flesh. After reaching the opposite end 
of the shell the bill is returned to one side of its starting point, 
and snips its way along a line adjacent.and parallel to the pre- 
ceding, and so on, until the adherent flesh has been removed 
from both valves. This skilful procedure is carried through 
rapidly without pause, and often without moving the shell. It is 
seldom seen towards the end of the feeding periods, and at these 
times shells are to be found in which portions of the mantle 
remain. 
Consideration of the methods employed by the Oystercatcher 
leads to the conclusion that fracture and rotation of the valves 
are in no way essential to the complete exposure of the contents 
of the shells. This view is supported by the cases in which 
neither occurs, and by the position, relative to the Mussel, in 
which the bill is introduced. It will be seen that the bill is in- 
serted in the posterior half of the commissure between the valves, 
and when the attack is made on the borders it is pushed down 
just in front of the posterior adductor muscle. In this position 
the bill separates the valves most widely where separation is 
most required. Observation proves that mere rotation of the bill 
between the valves is sufficient to rupture the fused portion of 
the mantle, and to impair the action of both muscles; they con- 
tract very slowly after slight extension. The wider separation, 
usually produced, tears the posterior muscle from its attachment 
to the valve, which forms the fulcrum of the lever, and the 
anterior adductor gives way in similar fashion whenever the 
valves are set farther apart. 
