THE AUSTRALIAN OYSTER. 123 



oysters imported from New Zealand. This experiment has proved as 

 unsuccessful as the laying down on such heds of our own rock oysters. My 

 theory is that our drift oysters, our mud oysters, and our rock oysters, 

 require their own special food. JSow, this is the real point on which I think 

 all oyster-culture has failed in these waters. It is now an established fact 

 that the ostrea edulis of Europe, its variety osirca horealis of the waters of 

 New York, its variety ostrea angasi of this coast, and the variety of ostrea 

 edulis, which also occurs on the New Zealand coast, all require a diatomatie 

 food for their existence. Other foods, no doubt, are consumed by these 

 oysters, such as the embryo forms of other molluscs, hydroids, bryozoa, the 

 larval forms of rhizopods and crustacean, and minute zoospores ; but living 

 diatoms form the principal element of their food. I have strong reasons for 

 saying that our drift oysters are dependent on a similar class of food for 

 their existence. I have not been able to convince myself that our rock 

 oysters are dependent on living diatoms for their existence. On the 

 contrary, the quantity of diatomatie debris extruded from them is remarkably 

 small. Their position appears to me to be well suited to enable them to live 

 on the larval forms of those classes which I have mentioned as forming part 

 of the mud oyster's food. If I am correct in my observations, this will go 

 very far to establish the fact that these rock oysters are not of the same 

 species as our drift oysters. 



Now, let me point out how this neglect of the study of the food of our 

 oysters has been the ijieans of preventing oyster-culturists from being success- 

 ful in establi-jhing new beds of oysters on ground which, to all appearances, 

 was well suited to the purpose ; but fresh water did not exist there, and 

 diatomatie life depends for its existence, to a great extent, on the presence of 

 fresh water. That intelligent observer, Mr. "Woodward, has almost come to 

 the same conclusion as myself without knowing the reason why, and has told 

 the public that oyster life depends on the salinity of the water. In former 

 days, when our mud and drift oyster-beds were in their prime, the land on each 

 side of our estuaries and inlets running up into our rivers and creeks was 

 thickly timbered and unfilled. On the banks of many of these estuaries 

 were situated pools of naturally-preserved fresh water — in fact, in some 

 instances, extensive lakes. Such reservoirs of fresh water have been got rid 

 of by removing the timber, thus allowing of evaporation, and by draining 

 them into the sea. Now, these reservoirs have really been the source from 

 which the diatomatie food of the oyster has been derived. Formerly the 

 water was conducted by some subterranean means into the bottom of the 

 estuaries of the sea, and there welled up; and it was around these sub- 

 aqueous springs of fresh water that the oysters developed in beds, and throve 

 so well. While influences have been at work to destroy this source of 

 diatomatie water supply, other influences have been at work to assist the now 

 starved-out oysters in dying off from their beds. The ground which was 

 recovered by clearing and drainage has been ploughed up for agricultural 

 purposes. The loose earth on the surface so ploughed up has been washed 

 into these estuaries, and has in many instances suffocated, as it were, the 

 oysters in their natural position. Such estuaries and rivers are continually 

 being stirred up by the screws and paddles of our steamships. The water 

 which flows over "the oysters is constantlj'- in a state of disturbance. The 

 stirred-up mud gets into their gills, and the animals have not power to expel 

 it. They have attempted to combat its offensive presence by throwing out a 

 nacreous shelly covering, which alarmists tell you is a new disease among our 

 oysters. This process of mud choking has not only occurred to oysters, but 

 also to all bivalves, as is too evidently seen in the destruction which has 



