[23] THE OYSTER AND OYSTER-CULTURE. 705 
the breeding-pond. But while the water is rendered clear by being al- 
lowed to stand quiet, yet by this means a large amount of organic mat- 
ter which serves as food for the oysters is taken from it. Especially | 
dangerous, however, to oyster beds within the dikes would be the cold 
during winter weather, for along our North Sea coasts the water is low- 
est during an east wind, and at the same time such a wind is accompa. 
nied by the lowest degree of temperature. Hence, at such times, when 
a great depth and a constant change of water over the beds would be 
the best protection from freezing, we cannot have high water, nor can 
the water then standing over the oysters be constantly changed; thus 
during every cold winter, a large number of oysters would be sure to 
perish in their beds. Even now, upon the shallow oyster-beds of our 
sea-tlats, oysters are frozen exactly in proportion to the depth of the water 
over them during these cold spells; the shallower the water the greater 
the destruction upon the beds during a severe winter. During the severe 
winter of 1863~64, when, on account of ice, no oysters could be taken 
from December 21 to February 17, and during the winter of 1864~65, 
when the fishing was interrupted from January 24 to March 26, dead 
oysters were found upon a large number of the banks. The greatest de- 
struction of oysters within the memory of the oldest fishermen took place 
during the severe winter of 1829~30, when Schleswig-Holstein was 
visited by an unusually low temperature, which continued from the mid- 
dle of November until the beginning of the next February. Most of the 
beds suffered greatly, and it was many years before they again recov- 
ered their former fruitfulness. In cold weather slime collects upon the 
gills and mantle-lobes of the oyster, the power of the muscles and cilia 
being weakened by the cold. Accordingly, the oyster is no longer in a 
condition by means of its rapidly-moving cilia, and the quick closing of 
the valves of its shell, to drive out the particles of slime brought in 
with the water. But the power of the cilia and the elasticity of the 
muscles are again restored as the water becomes warmer, providing the 
cold has not lasted too long. ‘The gills become clean once more, and res- 
piration and nourishment, which have been disturbed by the sliming, 
proceed again as before. If the cold spell is prolonged, then, in ad- 
dition to the sliming of the gills and mantle, there are yet other per- 
nicious results. The shell-muscle becomes so soft that it can no 
longer close the valves. The cilia move slower and slower, and finally, 
when the shell-muscle has allowed the valves of the shell to gape 
wide open, cease moving altogether. The mantle and gills become 
pale in color, infusoria nest in them and hasten their destruction, 
and soon their ciliated layer separates and disappears. The softest 
portions of the body, the generative organs, the liver, and the stomach 
quickly vanish, probably consumed by snails, crabs, worms, and star- 
fish as soon as they can make their way unhindered into the open 
shell. The last part of the mollusk which is to be found in the shell is 
the shell-muscle. It remains free between the two valves, or attached 
S. Mis. 29 45 
