354 Professor Huxley [May 11, 



There can be no doubt that the great mass of oysters in an oyster 

 bed may be removed by systematic and continuous dredging. But 

 those who are best acquainted practically with the nature of that 

 operation will be least inclined to believe that all the oysters on a bed 

 could be cleared off in this way, even if the attempt were made ; and, 

 as it must cease to be profitable to dredge long before the point of 

 entire clearance is reached, it is plain that, in practice, the attempt 

 will not be made. It may be doubted if ordinary dredging ever fails 

 to leave some thousands of oysters, great and small, on a bed of any 

 extent. 



Thus, if we admit, for the sake of argument, that an oyster bed 

 may be exhausted by ordinary dredging, the reason why the oysters 

 vanish is not ol)vious. For, sup230sing only a thousand oysters left, 

 they ought to suffice to restore the bed by degrees. I am aware that 

 it is said that, in the meanwhile, the enemies and competitors of the 

 oyster have got the upj)er hand, that the ground has been spoiled by 

 accumulation of mud and so on. But this reasoning leaves out of 

 sight the fact that the oysters have not been there from all eternity. 

 There was a time when there were no oysters on the ground, and when 

 the oyster larvfe immigrated, they fixed themselves there, increased 

 and multijjlied, in spite of all obstacles. Why should they not do so 

 again ? 



The question is further complicated by the consideration that it is 

 by no means certain whether the population of a given oyster bed is 

 kept up by the progeny of its own oysters or by immigrants. As I 

 have pointed out, it is ascertained that the larvae, even under very 

 unfavourable circumstances, may swim about for a week ; and it 

 has been estimated that they are ordinarily locomotive for two or 

 three times that period. Even if we supj)ose the average j)eriod of 

 freedom to be not more than three days, the chance that an oyster 

 larva will eventually settle within a mile of the spot at which it was 

 hatched, in any estuary or in the open sea, must be very small. For, 

 in an estuary, and almost always in the sea, one of the two alternating 

 currents of water is dominant, and a floating body will drift, on the 

 whole, in that direction, often many miles in the course of a day. 



The opportunity of observing the natural formation of a new 

 oyster bed is rare, but the details of the process have been carefully 

 watched in at least one case. Uj) to the year 1825, the Limfjord in 

 northern Jutland consisted of a series of brackish water lakes com- 

 municating with one another, and opening on the east into the 

 Kattegat. In the last century, unsuccessful attempts were made to 

 plant them with oysters. But, on the 3rd of February, 1825, a great 

 storm broke through the dam which separated the western part of the 

 Limfjord from the North Sea ; in consequence of this, the water of 

 the fjord became gradually Salter, the brackish water plants and 

 animals disappeared and North Sea animals took their places. Among 

 these, in 1851, oysters were observed, and, year by year, they extended 

 over a larger area. In 1860, only 150,000 were taken ; at present. 



