43 



detroquage. By their use the brood-oysters damaged 

 during this operation and those whose growth on the 

 tiles has been retarded through crowding- unfavourable 

 situation or the juxtaposition of competing organisms 

 (mussels, ascidians, barnacles, etc.) experience improved 

 conditions and at once respond by immediate increase in 

 the rate of shell growth. The construction of the case and 

 the manner it is raised above the ground enable the 

 young oysters to experience the full benefit of the water 

 movement set up by the action of the tides ; the current 

 passes not only over them as when they lie free upon 

 the surface of the park, but also beneath and betwixt 

 them, hurrying food to every gaping mouth. Danger 

 from partial suffocation by mud, and from the ravages 

 of enemies, whereof the name is legion when the oysters 

 are young, are largely eliminated automatically by the 

 form and position of the cases ; the parker also contri- 

 butes much to this immunity by constant attention to 

 the well-being of the contents. As frequently as possible 

 he visits the cases, clears away whatever sea-weeds and 

 rubbish may have attached to or lodged within the cases, 

 washes off mud, and, most important item of all, rear- 

 ranges and relevels the brood-oysters themselves, that all 

 in turn may have the advantages of forming a portion 

 of the uppermost layers. Here I must mention that 

 economy forbids the oysters to be spread thinly in the 

 cases. When quite young they are often disposed quite 

 three inches in depth ; only by constant visits to turn and 

 rearrange the dense mass can health and rapid growth 

 be ensured. The advantages of case-culture are so 

 emphatic in ensuring rapid growth and so enabling the 

 " crop " to be placed on the market at a much earlier date 

 than when the oysters be laid free on the general surface 

 of the park, that in the heyday of the Arcachon oyster 

 industry in the early nineties, the parkers carried case 

 culture much further than is done now. In those days 

 every parker had large numbers of cases in order to 

 prolong the term of sojourn in these sanctuaries. About 

 i8q6 the number of cases in use in the basin was estimated 



