Ee ee. eee 
Mr. Howard Martin on Oysters. 195 
that is the case with Ostrea edulis; but it appears to be estab- 
lished that the eggs of O. angulata are fertilized and hatched in 
the water after having been emitted. Oysters are unfit for 
eating and said to be ‘‘milky” when the eggs begin to form in 
the gland, and “white spat’? is the name given to embryo 
oysters before being emitted from the mantle of the parent. 
Black spat is the perfect larval form of the oyster, having a 
kind of retractile cushion or pad furnished with cilia used for 
swimming, and a funnel-shaped collar. At this stage they are 
emitted from the parent. The eggs, when lying in the mantle, 
oval clusters of globular atoms floating in a transparent 
iquid. 
It is said that an oyster occupies about a week in ejecting the 
whole of its spat; this is done by quickly opening and shutting 
the shells. Mr. Frank Buckland calculated that an oyster pro- 
duced from 276,555 to 829,665 spat in a season, and there must 
therefore be enormous waste of young oyster life to account for 
the comparative scarcity of oysters. Spat is emitted in May, 
June, July, and August in British waters, but it is probable that 
the greater part of spat emitted in those waters, after the early 
part of July, dies for want of the warm still weather necessary 
in the first stages of its existence. Spat having been emitted, 
at once rises, and often floats a considerable distance, e.g. young 
oysters are usually found in the flats outside Whitstable, in the 
estuary of the Thames, which have floated as spat from the 
stock of oysters in-shore; and it is said that an oyster-bed out- 
side Shoreham was established by spat from oysters stored in 
the harbour-beds. It is impossible to say how long the spat 
floats in freedom, owing to the great difficulty of tracing spat to 
its final settlement. After a time the spat sinks, possibly from 
the development of the shells altering its specific gravity, and 
attaches itself to any clean hard surface with which it comes 
into contact. The various substances provided for this purpose 
in oyster fisheries are called “collectors.” The attachment is 
made by the secretion which forms the shells of the oyster, 
which acts as a kind of cement, and ‘‘sets’’ on to both the shell 
of the spat and its resting-place. 
Floating spat is easily killed by cold: a temperature of 44° is 
fatal; 65° or 72° is most favourable to itsdevelopment. Floating 
spat is exceedingly sensitive to any change of condition round 
it. It always sinks to the bottom at the sound of thunder, and 
it is said that a prolonged storm usually kills it. Shrimps and 
small fish eat large quantities of floating spat. Shrimps, gobies, 
and young mullet will lie by the parent oysters in the spatting 
season, and eat the spat as it is emitted. In open beds im- 
mense quantities are carried away by tides and currents, or 
strong winds. 
