[65] THE OYSTER AND OYSTER-CULTURE. 147 
hence it would be more correct to estimate the minimum size for mark- 
etable oysters according to the average thickness of the shell than ae- 
cording to its breadth. Estimated thus, a thickness of shell of 18 milli- 
meters would be a judicious minimum size for the Schleswig-Holstein 
oysters. In conclusion, I hereby give, as a foundation for all oyster- 
culture, the most important rules for the preservation and improvement 
of natural oyster-banks. 
An oyster-bank will give permanently the greatest profit if it pos- 
sesses such a stock of full-grown oysters as will be sufficient to maintain 
the productiveness of the bank in accordance with its biocénotie condi- 
tions. 
Whenever the natural conditions will admit of it, the yielding capa- 
city of an oyster-bed may be increased by improving and enlarging the 
ground tor the reception of the young oysters. 
The natural banks should be improved by removing the mud and 
sea-weeds with dredges and properly constructed harrows, and by seat- 
tering the shells of oysters and other mussels over the bottom. When 
circumstances will permit, all animals which are taken in the dredge, 
and which kill the oysters or consume their food, should be destroyed. 
It would be much more judicious, and much better for those who eat 
oysters, if the close-time could be extended until the 15th of September 
or the Ist of October, so as to allow the oysters sufficient time, after the 
expulsion of the contents of the generative ®rgans, to become fat before 
being brought to the table. 
If it is desired that the oyster banks should remain of general advan- 
tage to the public, and a permanent source of profit to the inhabitants 
of the coast, the number of oysters taken from the beds yearly must 
not depend upon the demands of the consumers, or be governed by a 
high price, but must be regulated solely and entirely by the amount of 
increase upon the beds. 
The preservation of oyster-beds is as much a question of statesmanship 
as the preservation of forests. 
