654 OYSTERS, AND ALL ABOUT THEM. 



connection with the sea by means of canals. Where these 

 canals cut through the dyke it would be necessary to build 

 a gate, in order to prevent the sea-water from passing in 

 during high tide. Then, oyster-beds could not be laid 

 down in the neighbourhood of this gate, because it would 

 serve not only as an inlet for salt water, but as an outlet 

 for the fresh water from the marsh-land, and so fresh 

 water instead of sea-water would cover the oyster-beds. 



. . . . (In these beds) It is certain that they will 

 not receive as much food as in the open sea, since they 

 cannot have nearly as much water as will pass over them 

 upon the natural beds ; and the quantity of nourishment 

 varies in proportion to the amount of water which passes 

 over the beds. In these beds the oysters would also be in 

 danger of being buried in the deep mud, and in order to 

 prevent this they must either be changed very often into 

 clean beds, or else a cleaning pond must be formed 

 beside the breeding pond. But while the water is rendered 

 clear by being allowed to stand quiet, yet by this means a 

 large amount of organic matter which serves as food for 

 the oysters is taken from it. Especially dangerous, how- 

 ever, to oyster beds within the dykes would be the cold 

 during winter weather, for along our North Sea coasts the 

 water is lowest during an east wind, and at the same time 

 such a wind is accompanied 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. 



. . . . In cold weather slime collects upon the 

 gills and mantle-lobes of the oyster, the power of the 



