404 OYSTERCATCHER AND TURNSTONE 



borders ; these, unlike those opened from the dorsal side, seldom or 

 never exhibit damage to the margins, and many are opened without 

 fracture of the valves. Mussels opened through the posterior ends 

 are never fractured, although there may be slight comminution 

 of the thin edges of the valve where the bill enters. The pro- 

 cess of opening is comparatively simple : after the bill has been 

 inserted and pushed home, vigorous shaking sideways effects an 

 opening. 



As a rule mussels are detached from their anchorage before 

 extraction of the contents takes place. If the ventral border is 

 exposed, opening takes place before detachment, but when entrance 

 is gained through the dorsal borders, the valves are first separated 

 slightly, and opened up after the shell is detached. There is good 

 reason for this distinction, as the mussel rests more securely on the 

 ground on its rounded ventral surface than on the thin dorsal edge. 

 The oystercatcher effects detachment of the mussel by gripping one 

 valve between its mandibles the upper one inside the shell and by 

 giving a few vigorous shakes and an upward pull. 



Throughout the entire process of opening the shells and clearing 

 out the contents, the oystercatcher shows considerable celerity and 

 skill. The knife of an expert oyster-opener is not used with more 

 certainty and familiarity with the anatomy of the mollusc operated on 

 than is the bill of the oystercatcher in dealing with a mussel. The 

 posterior and anterior adductor muscles are cut through as the bill 

 is thrust vertically down between the borders of the valves, and in 

 a way that, as Mr. Dewar says, " goes far to prove that the oyster- 

 catchers are acquainted with the position and relative importance 

 of the two muscles, and fully realise the necessity for their early 

 destruction." After the bulk of the mollusc has been removed and 

 swallowed, the bill, used like a pair of scissors, starts at one end of 

 a valve and snips away the portions of the mantle still adhering to 

 the shell. "After reaching the opposite end of the shell, the bill 

 is returned to one side of its starting-point, and snips its way along 



