FOOD AND FEEDING OF OYSTERS. 



1301 



Fig. 3. — Cross section 

 at A, figure 2. 



long, the water inclosed is a vertical column of the stratum lying between 2 

 inches and 12 inches above the bottom, and as the currents do not flow over 

 the beds in horizontal strata, but roll over and over, this specimen is regarded 

 as a fair sample of that in which the oysters are bathed. 



The instrument is now used in Massachusetts, Maryland, Virginia, and Loui- 

 siana, and actual tests have shown that it takes a water speci- 

 men much cleaner and freer from mud and extraneous materials 

 than do the instruments previously employed. 



The other defect of the old method of determining the food 

 value of oyster-producing waters arises from the practice of using 

 the number of diatoms or organisms per liter as the measure 

 of their productiveness. It is well known that diatoms, which 

 usually constitute upward of 95 per cent of the food of oysters, 

 differ greatly in size and the species vary in comparative abund- 

 ance in different regions and from season to season in the same locality. When a 

 numerical expression is employed, it follows therefore that a multitude of small 

 organisms may give an apparent superiority to a water specimen as compared 



with another containing a 

 n/>^/e;yo/^(^ smaller number of a spe- 



cies of vastly larger size and 

 much greater aggregate vol- 

 ume, and my own ex- 

 perience has shown cases 

 where this error amounted to 

 nearly 400 per cent. The 

 method is attended with 

 grave error as applied to 

 even limited regions and is 

 wholly untrustworthy as a 

 basis of comparison between 

 widely separated localities. 

 It gives seemingly quanti- 

 tative results, but these, not 

 being volumetric, are decep- 

 tive. 



Direct volumetric deter- 

 mination can not be made 

 on account of the presence 

 of considerable volumes of sand, mud, and extraneous debris in the filtrate, 

 these materials greatly exceeding the food organisms in volume. Grave 

 attempted to overcome the difficulty by listing the food organisms by species, 



M^ 





£>7i////ejra^@ 



Fig. 4. 

 Details of tripping device of water specimen cup in figures i and 2. 



Fig. s- 



