208 THE ZOOLOGIST. 
into the sand and the Mussel is opened in one or more of the 
ways which have been described. 
It is probable, as Macgillivray* suggested in the case of he 
Dunlin, that ‘‘ they discover the object of their search rather by 
the kind of resistance which it yields than by touch like that of 
the human skin.” Sand overlying smooth rock is equable to the 
touch, and I have noticed that the tapping instrument meets 
with greater resistance over the presenting border of a Mussel 
than elsewhere, but I have not been able to distinguish a Mussel 
from inanimate objects. Possibly the movement which the 
Mussel makes in closing its valves and drawing them more 
nearly to the rock is transmitted to the bill through the sand; 
the high proportion of hidden Mussels opened through the 
ventral borders, together with the circumstance that the relative 
frequency of the several positions assumed by the Mussel is 
not influenced by the presence or absence of overlying sand and 
mud, leads me to believe that it is so, and the movement which 
apprises the Oystercatcher of the presence of its prey often 
defeats the end in view, unless the ventral border of the Mussel 
is open to attack. 
At these times delicate imprints made by the point of the 
bill are seen on the sand or mud around the scalps. Usually at 
wide and unequal intervals, in places they are crowded together, 
and there may be a few shallow probings, some of which are 
bridged by septa of sand or mud, showing that the mandibles 
are slightly separated. In several places these clear imprints 
are obliterated by footmarks, often deeper than usual; in the 
centre of each place there is a deep conical pit surrounded by 
ejected material, and the empty shell lies at the bottom, or it is 
found near by. 
The Oystercatcher removes the Mussel from its anchorage 
under the sand or on the open banks from choice, or as the 
result of the undesirable attention of others, and to avoid the 
prolonged submersion of the head under water which extraction 
of the contents sometimes requires. A fine distinction is drawn 
between the shells of the two classes. Those which present the 
ventral borders are opened up before being detached from their 
foundations, while those in which the dorsal borders are present 
* ¢ History of British Birds,’ vol. iv. p. 212. 
