124 THE AUSTRALIAN OYSTEE. 



taken place in the beautiful trirjonias of our harbour, and in the large 

 handsome-frilled Venus which once existed in such profusion in the Parra- 

 niatta Kiver, but which now, like our drift and mud oysters, has been almost 

 absolutely wiped out, although it has never been used as an article of 

 food. 



In support of my theory that the destruction of our bed oysters is caused 

 by the two influences which I have mentioned, and others which I could 

 give, I make the following quotations from " The Food of the Oyster ; its 

 Conditions and Variations"- — by Mr. Bashford Dean, A.B., published in 

 the supplement to the Second Report of the Oyster Investigation and of 

 Survey of Oyster Territory of the State of New York for the years 1885 and 

 1886 :— 



" AVater was collected from several beds selected and examined forty-eight 

 hours after it was taken. The food of the oyster, together with its conditions 

 and variations, was noted in each specimen. Not only was the quality of 

 the food of the oyster examined, but also the proportions of the different 

 kinds of minute plants and animals of which it was composed. The end in 

 piew was to ascertain the variation in the amount of oyster food, and the 

 abundance or scarcity of the miscroscopic life which controls the condition of 

 the oyster ; the effectof season, weather, temperature, and general condition 

 of the water as affecting the oyster and its food. This essential information 

 regarding the most favourable conditions for oyster cultivation, all of which 

 would be of value to the planter in selecting and managing his oyster 

 grounds, had heretofore been scarcely touched upon. All work in the 

 direction of increasing the supply of oysters must include information 

 regarding its living. Much as we owe to Dr. Brooks, Professor Eyder, and 

 Professor Rice for their researches in regard to the life history and embryo- 

 logy, much farther investigation will be required before its hygiene can be 

 understood ; for even the oyster may have its conditions of welfare depen- 

 dent upon food, weather, and locality." 



""What we want to know is the principal local varieties of its food ; the 

 proportion or relative prevalence of the different forms of its food, and the 

 fresh and salt water differences ; the condition of the oyster-bed waters, 

 especially as to the amount of oyster foods they contain ; the causes of the 

 variations of the oyster food in oyster-bed waters as affected by season, 

 temperature, and weather ; why oysters fatten by immersion in fresh water ; 

 and how the colour of food organisms affect the appearance of oysters. 

 "The food of the oyster," says Professor Eyder, "consists entirely of 

 microscopic beings and fragments of organic matter, which are carried by 

 currents from the palpi and gills to the oyster s mouth at the hinge end of 

 the shell. This food when once in the mouth is carried by the action of 

 cilia down the gullet to the stomach, where they undergo digestion and 

 solution. Along with the food much indigestible dirt is taken in, and is 

 cast out with the refuse and waste from the body. This refuse and waste 

 material shows that the oyster subsists largely on diatoms, a low type of 

 moving plants, which swim about in the water, incased in strong boxes. 

 When passed out the living contents have been dissolved out of these diatom 

 eases by the juices of the stomach. Besides diatoms, the spores of alga?, 

 the larva) of sponges, bryozoa, hvdroids, worms, and other molluscs are 

 taken in as food by the oyster at the heads of the small creeks or inlets. 

 Where the water was but little affected by the tides a relative greater 

 development of such minute forms was found." 



