SEA MUSSEL MYTILUS EDULIS. 200. 



Percentage Composition of the Dry Substance of Land Crops. 



Ordinary meadow hay 

 Good meadow hay - 



Rye (grain) 



Peas 



Potatoes 



Protein. 



Fat. 



Carbo- 

 hydrate. 



_ 



8.7 

 136 

 11. 8 

 26. 4 



8.4 



836 

 75° 

 82.3 

 68.2 

 87.2 



Ash. 



S-8 

 8.2 

 2. I 

 3- I 

 3.6 



Because of their silicious skeletons, the diatoms show a small proportion of protein 

 with a high percentage of ash. Samples, however, containing many such Protozoa as 

 Ceratium will have a composition similar to rye or good meadow hay. It is on this 

 evidence that many persons have concluded that diatoms and, to some extent, such 

 Protozoa as the peridineans, represent the ultimate source of marine food supply. As 

 Moore (1910) has remarked, it is this invisible vegetation of our bays and estuaries 

 which, useless to man in its original state, is annually converted into oyster flesh worth 

 $18,000,000. In fact there is good evidence for believing that the total value of our 

 entire fisheries products is derived, in large measure, from this source. So great is the 

 economic value of this group of plants that it has been made a subject of important 

 investigation by the Governments of many nations, including England, France, Germany, 

 Denmark, and the United States. 



The most recent advances in methods for determining quantitatively the available 

 amount of these food organisms in the water, such as are utilized by the oyster, have 

 been made by Moore (1910), who devised a bottle which has a capacity of a little more 

 than a liter and can be filled in such a way as to " inclose 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, ' it roll over and over, the specimen is regarded 

 as a fair sample of that in which the oysters are bathed." A liter of this sample is con- 

 centrated in 10 cc. of water by filtration through sand or precipitation in an Erlenmeyer 

 flask after the addition of a little formalin. The filtrate is then agitated and a measured 

 quantity transferred to a Rafter cell, where the organisms are listed and counted by 

 species and a calculation made of the total number of each per liter. Careful measure- 

 ments of the length, breadth, and thickness of each species are made based on Van 

 Heurch's "c. d. m." (0.01 millimeter) as a unit of measurement, the unit of volume 

 being the cube of this, "cu. c. d. m." (0.000,001 cubic millimeter). By this means a 

 fairly accurate measurement of the actual bulk of the organisms present in a given 

 volume of water can be made. 



Using this method in connection with careful measurements of the stomach con- 

 tents of oysters and the amount of water they are able to filter, Moore (191 3) was forced 

 to the surprising conclusion that "the volume of living food is insufficient to account 

 for the actual growth of the oyster, making no allowance for the requirements of the other 

 vital activities." Such investigators as Putter, Petersen, Blegvad, and Jensen are of the 

 same opinion and claim to have found other equally important sources of food supply 

 for the marine fauna. Putter (1907 and 1908) maintains that the sea is an immense 

 reservoir of foodstuffs in the form of dissolved organic carbon and nitrogen compounds 

 on which many marine animals actually feed as saprozoic creatures. His investiga- 



