CONSERVATION AND INCREASE OF PRODUCTION 109 



such that the culturist who rears the oysters for market buys his seed 

 from the spat collector. 



The natural banks are of importance chiefly in the production of seed 

 oysters, which may be procured by dredging. But by far the greatest 

 amount of seed is caught on tiles that, because of their size, shape and 

 weight, are well adapted for this purpose. They can be built in layers 

 crossing each other, with the concave side down, so that the water con- 

 taining larva? can readily pass among them and the under surfaces remain 

 free from sediment. They are white- washed with a thick layer of lime- 

 and-sand cement, so that when the spat are of sufficient size or begin to 

 crowd one another for space in growing, they can be easily chipped off 

 without destroying the tiles. Attempts have also been made to procure 

 spat by constructing breeding ponds, by hollowing out and walling in 

 portions of salt-marshes, and placing in them great numbers of spawn 

 oysters. The ponds were sometimes provided with flood-gates, so that 

 the water could be drained off at ebb tide for cleansing purposes, and refilled 

 when required at flood tide. In some years considerable success has been 

 achieved, but it could not be depended upon. Thin, flat, wire cases are 

 extensively used in which the young spat may be retained in numbers, 

 protected from their enemies, or raised above the interference of mud and 

 sediment. Muddy bottoms are adapted to cultural uses by spreading 

 sand and gravel over the surface until a crust is formed. Oyster parks, 

 made by enclosing tracts of tide land by planks, or other barriers sufficient 

 to retain shallow water for a few hours, or more expensive stone-walls 

 with flood-gates, furnish areas of suitable warmth and food supply and 

 serve to protect against enemies and shifting sand or mud. Claires, 

 large or small excavations on marsh or meadow lands, containing a few 

 feet of muddy water and banked by earth or sods are employed to fatten, 

 flavour or colour the marketable oysters. The water is changed only 

 every week or two, contains a great amount of sediment, is badly aerated, 

 warm and salty, and is thick with diatoms, one of which (Amphipleura 

 ostrearia) communicates a greenness to the oysters feeding upon it. The 

 green oysters of Marennes have long been famous. Growth is forced but 

 there is a high mortality. 



Two other processes are employed in France — disgorgement and educa- 

 tion. For the first the oysters are placed on a hard bottom in clean water for 

 a few days, in order to permit a discharge of the black muddy contents of 

 the intestine before marketing. For the second they are accustomed to 

 short periods of exposure out of the water, in order to teach them to 

 tighten their shells and retain their fluids during shipment. 



In Holland the oyster has been the subject of careful study, and oyster 

 culture has since 1870 been very successful. The limited areas, the leasing 

 by auction for a number of years, the active competition, the frugality 

 of the people and other causes, have contributed towards this. The 



