204 BULLETIN OF THE BUREAU OF FISHERIES. 



day for three days the discharged feces were carefully picked up with a pipette and 

 placed in a graduate with a few drops of formalin to prevent decomposition. When 

 the material had settled completely the quantity was read off. The observed result 

 was that 75 mussels discharged a daily average of 3,065 c. mm. of digested matter, or 

 40.8 c. mm. for each individual. This means that the volume of solid food actually 

 consumed by a 3-inch mussel is not less than 40.8 c. mm. per day and probably is con- 

 siderably more. This brief series of observations is too limited to form the basis of any 

 conclusions as to the amount, kind, and quantity of food utilized by the mussel, but 

 it suggests a means for solving the problem. What is required is that the observations 

 of this sort be made to cover a long period and be supplemented with chemical analyses 

 of stomach contents and feces to show the quantity of carbon and nitrogen absorbed 

 in a given time. 



Whether or not the phytoplankton and detritus constitute the entire food of the 

 mussel we do not know at present, but that there must be an enormous supply of food 

 materials available in the sea is demonstrated in a most striking way to one who 

 witnesses the appearance and rapid growth of a bed of sea mussels on vast areas of 

 the sea bottom, sometimes hundreds of acres in extent. In three years time this 

 shellfish may attain a length of 3 inches and cover the ground to the amount of more 

 than a bushel to the square yard. This phenomenal growth indicates that the mussel 

 must be fed from some great and constant source of food supply for, according to the 

 well-known physical laws, neither matter nor energy can be created or destroyed. The 

 source of the enormous amount of matter and energy represented in a 3-year-old 

 mussel bed presents a most interesting problem upon which much light has been thrown 

 but which, as stated above, has not been completely solved. To appreciate the prin- 

 ciples it is necessary to compare the conditions of life as they are found on land and 

 in the sea. 



On the land the most conspicuous form of life is vegetation. Almost everywhere 

 the land presents a vast expanse of verdure consisting of green plants of all sizes from 

 the minute algae to the giant trees. They represent a particularly important organiza- 

 tion in that, as distinguished from animals, they have the power of uniting solar energy, 

 water, the common salts of the earth, and gases of the air into the food principles which 

 supply not only the needs of the plants themselves but provide also for the existence 

 of all forms of animal life. The animals are, for the most part, herbivorous. Carnivora 

 are necessarily few in number, for if it were not so they would soon destroy the Herbivora 

 and thus bring about their own extinction. Green plants, therefore, furnish the ultimate 

 source of food supply for terrestrial organisms. 



In the ocean, life conditions are found to be quite different, although, as we shall 

 see, the relations are the same in principle as for those on land. Vegetation, however, 

 is as inconspicuous in the sea as it is conspicuous on the land. A fringe of seaweed 

 may be found along the coast and some rather extensive masses of alga?, such as the 

 Sargasso sea, may be found floating in the middle of the ocean ; but taken as a whole the 

 ocean is barren of visible vegetation. Under these conditions there can be very few 

 or no animals that correspond to the terrestrial Herbivora. A few fishes may browse 

 on the seaweeds which fringe the shore or float in the water, but they are not numerous. 

 Most of the marine animals commonly seen are carnivorous and voracious beasts of prey. 

 The larger species devour the smaller ones, and these in turn feed upon those smaller 



