1888 - 89 .] Mr D. M‘ Alpine on Bivalve Molluscs. 
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Part III. — In the Oyster. 
Ostrea glomerata , Glas.; 0. edulis , Linn., var. purpurea , Hanley. 
In the oyster the left valve of the shell is thick and convex ; 
it is on this side that the oyster usually rests. When unattached, 
however, there is some difference of opinion as to its position. 
In a recent number of Nature (12th April 1888) a summary of 
a Report from the British Consul at Baltimore on the Oyster 
Fisheries of Maryland is given, in which the oyster is said to 
feed twice a day, always at the still moment preceding the turn 
of the tide; and at no other time, except when feeding, or rather 
taking in food, does it open its shell. It feeds on the liquor in 
the shell, this habit necessitating the convex or left valve being 
lower, to retain the liquor in sufficient quantity. 
Even when the shell is closed the liquid inside will be in 
circulation, owing to the action of the cilia, but with the im- 
portant difference that the energy of the cilia, under these circum- 
stances, is probably less, for, as will be fully shown in the sequel, 
the cilia-bearing part can increase or decrease the expenditure of 
energy. Professor Semper mentions ( Animal Life , p. 147) having 
eaten oysters, which although with a salt flavour and bathed with 
brackish water at high tide, at ebb tide were surrounded with a 
rapid stream of drinkable fresh water, and opened their shells to 
it. He gives a drawing of this oyster living in spots where the 
water is quite fresh, and it is noteworthy that he should find that 
these oysters opened their valves at the turn of the tide. The 
most highly prized oysters in New South Wales are likewise those 
taken from beds where fresh and salt water mingles at certain 
seasons of the year. The movements of the parts of the oyster 
may help to explain some of its habits and to show the differences 
between the lower and upper side. In the following brief account 
of the three motile parts — palps, gills, and mantle-lobes — as well 
as of the entire shell-less animal, the rock oyster will always have 
precedence, since the results were decided and satisfactory on the 
whole ; the movements of the mud oyster will be added as con- 
firmatory. Any general description of parts is likewise given from 
the rock oyster. 
The rock oyster of Sydney is 0. glomerata , Gould. “The 
