THE AUSTRALIAN OYSTER. 125 



" In order to examine the food of oysters it is requisite to obtain oysters 

 freshly raked from their beds, aud at once to inspect, by the microscope, the 

 undigested contents of the oysters' stomachs. They should be taken from 

 the beds at a three-quarter flood tide ; for the greater part of the oyster 

 feeding is then completed. Twenty-four hours after oysters were taken from 

 the bed I found live crustaceans in the stomach. I found also varieties of 

 diatoms and three forms of desmids, which are regarded as existing only in 

 fresh water, although the water from which these oysters were taken was 

 thoroughly salt — sp. gr. 1018 — I am inclined to conclude that their presence 

 tended to prove the entrance of fresh water on their beds. These desmids, 

 it is true, had all their fresh-water brilliancy ; and the explanation I offer is 

 that the springs and streams of fresh water come up from the bottom at the 

 bed where the oysters thrive, and permits some of the more hardy of these 

 fresh-water forms to live. Among the microscopic forms I noted were 

 rolifers, crustaceans, protozoa, and rhizopods. Living water-fleas and other 

 allied forms were repeatedly taken from oysters which had been twenty-four 

 hours out of water. This indicates that these larger forms are not properly 

 the food of oysters. If they had been they would have been killed and 

 digested in a much shorter time. I think the animal portion of the food of 

 oysters consists rather of larva forms or rhizopods, cyprides, and kindred 

 crustaceans ; also the ova and young of small molluscs, and the lower stages 

 of hydroids and bryozoa. But the principal element of oyster food consists 

 of single-celled low-lifed plants, such as desmids — entirely fresh-water forms 

 of vegetable life — and diatoms. The latter constituted at least SO per cent, 

 of the total amount of oyster food, mostly marine examples. Portions of 

 sea-weed in minute broken fragments are found in the stomachs of oysters, 

 as also are oogonium of some of the oospores and minute zoospores. The 

 proportion of animal to vegetable life found was in 100, diatoms 88, desmids 

 about 1, spores and particles of seaweed 3, crustaceans, vermes and larval 

 forms 8. Many of the diatoms were recognised as fresh-water forms ; and 

 their presence points to an important fact in connection with oyster culture. 

 Throughout the Long Island beds there is a greater quantity of fresh water 

 continually present than would naturally be supposed. The presence of 

 desmids, wdiich belong entirely to fresh water, suggests the presence of fresh 

 waterstreams entering the harbour, and flowing several hundred yards without 

 becoming salt. This furnishes a practical hint as to selecting suitable grounds 

 for laying down and cultivating oysters, as well as to the position of building 

 and keeping ponds for their culture. Moreover, it gives us an insight 

 into oyster needs and requirements for a rapid growth and production of 

 oyster food." 



"It is a most important point to consider the kind of fresh water and the 

 quantity of it which should be admitted to oyster ponds and beds. As far 

 as possible'a moderate supply of ditch or spring water should be continually 

 kept entering such ponds to supply food. I am not advocating brackish 

 water for the cultivation of oysters, but rather the imitation as nearly as 

 possible of the bed water from which the oysters examined were taken. In 

 the case of the Long Island waters we shall have to provide for the entrance 

 of more or less fresh water into thetn. Along the shore of Long Island a 

 density of 1'017 or 1'018 is sufiicient. The most serious defect in our oyster 

 ponds is the neglect to provide for the entrance of sufficient fresh water into 

 them. Its presence in proper quantity increases the amount of diatoms for 

 food ; and it also maintains an unvarying density by compensating for the 

 loss caused by evaporation. This alteration of the density of the water is 

 injurious to the propagation of diatoms, aud is in a marked degree fatal to 



