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{/) Enemies and Diseases. 



Man himself is and has been the qreatest devastator 

 of oyster beds ; at the present time his reckless and 

 short-sighted fishing has actually destroyed practically all 

 the crreat natural beds on the French and English coasts 

 which about the middle of last century were being dredged 

 over by hundreds of oyster smacks in the season. A few 

 odd remnants alone are left, the most important, that of 

 Cancale, being kept in existence solely by stringent State 

 regulations and the limitation of the fishery to one or two 

 days in each season. 



In regard to oysters under cultivation the enemies are 

 those normal to shallow water natural beds, in some cases 

 aggravated and in others diminished, by the conditions 

 of culture. Boring molluscs, starfishes, crabs, predatory 

 fishes, and tunnelling worms and sponges comprise the 

 list of active enemies ; mussels, sponges, ascidians and 

 other attached or crusting invertebrate growths together 

 with sea-weeds of various species form a second category, 

 that of passive enemies — which by excessive competition 

 for the microscopic food in the water or by stifling over- 

 growth may entail as wide-spread injury at times as the 

 inroad of the battalions of active foes. Apart too from the 

 actual injury caused from time to time the precautionary 

 measures rendered necessary to safeguard the parks and 

 minimize the risks arising from these dangers involve 

 heavy and constantly recurring expenditure, special 

 measures of defence having to be taken against each of 

 the principal classes of depredators and parasites. 



Boring molluscs- -The species responsible for almost 

 all the loss from this class of enemies is a small species 

 of Murex, a genus of gastropod molluscs noted for their 

 carnivorous habits. Their mouth parts include a lone 

 ribbon carrying hundreds of narrow rows of very touo-h 

 and sharp horny teeth ; by means of these teeth the 

 little mollusc — it is scarcely an inch in length — can bore 

 through the thickest and hardest shells, the wear of the 

 teeth at the front end of the ribbon being made good by 



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