30 
The restriction of the oysters to certain points does not 
appear to depend upon the supply of food, or upon the char- 
acter of the water, but almost entirely upon the nature of the 
bottom. The full-grown oyster is able to live and flourish in 
-soft mud, as long as it is not buried too deeply for the open 
edge of the shell to reach above the mud, and draw a constant 
-supply of water and food onto the gills. The placing of 
adult oysters upon such bottoms at convenient points, to 
u fatten ” for the market, is a well-known practice. The oys- 
ter embryo would be ingulfed and smothered at once if it 
should settle down upon such a bottom, and in order to have 
the least chance of survival and long life the young oyster 
must find some solid substance to fasten itself to, in order to 
preserve it from sinking in the soft mud or from being covered 
by shifting sand or gravel. As soon as the young oyster finds 
'such a solid body, rough and clean, it fastens one valve of its 
"shell to it by secreting a cement of shelly matter around the 
growing edge. 
The living and dead shells of the adult oysters furnish the 
best surfaces for the attachment of the young, and for this 
reason the points where oyster beds are already established 
are those where the young have the most favorable surround- 
ings and the best chance for life, and the beds thus tend to 
remain permanent and of substantially the same size and 
"shape. 
At the time of attachment the shell of the young oyster is 
still very thin and delicate, and the animal falls an easy vic- 
tim to the numerous enemies which abound upon the oyster 
beds, such as crabs of various sorts, carnivorous gasteropods 
and various fishes. 
It is not an uncommon thing for fifty or a hundred young 
"“spat” to attach themselves to one full-grown shell. Some 
-of these are killed by enemies, and others are crowded out, 
so that only a few grow up at the expense of the others, and 
the number which survive is astonishingly small. Mobius 
has made an attempt to ascertain what chance of survival the 
newly-hatched oyster has. The ratio between half-grown and 
-adult oysters in the oyster beds of Schleswig-Holstein has 
