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THE AMERICAN MUSEUM JOURNAL 



breathing function of the gills is merely 

 secondary. The gills have developed 

 great brushes of cilia and have been 

 modified to serve primarily in the collec- 

 tion of food. Rapid movement of the 

 cilia causes a continual flow of water, 

 from which the cilia sift out enormous 

 numbers of diatoms, Protozoa, and mi- 

 nute floating particles of dead organic 

 matter, which are conveyed to the 

 mouth through a special food groove 

 located on the lower edge of the gills. 

 The process goes on day and night and 

 the food supply is practically inex- 

 haustible. Even though the members 

 of a community in a favorable situation 

 are packed together as closely as sar- 

 dines in a box, there is usuallv food 



Photomicrograp}! of the main hyssus f,'l<ni'l. showing 

 the glandular memhranes that hang down in the byssiis 

 cavity Hke a series of curtains. The sticky secretion 

 is forced out througii the aperture at the base where, 

 on coming in contact with the sea water, it hardens 

 into a tough rod 



enough for all as long as the avenue to 

 the inhalant canal remains unobstructed. 

 In very crowded portions of a community 

 it is often necessary for the members to 

 stand on their heads in order that the 

 individual food streams be not impeded. 



The food supply of the mussel com- 

 munity is a subject of great interest 

 because it represents the ultimate food 

 basis of all marine animals. Decaying 

 eelgrass forms minute particles called 

 "detritus," that contain nutritive com- 

 pounds related to starch, which the mus- 

 sel utilizes to some extent, but the most 

 important source of its food is the group 

 of plants constituting the diatoms. 

 They represent the energy of sunshine 

 combined with air, water, and salts in a 

 form available for food. In their com- 

 position the three food principles, pro- 

 tein, carbohydrate, and fat are present 

 and they are built up at a rate that is 

 astonishing and beyond our powers of 

 comprehension. Submerged in a me- 

 dium where they are supplied with un- 

 limited quantities of water, oxygen, and 

 mineral salts, and with sunshine, the dia- 

 toms are able to multiply and grow at a 

 rate that puts the proverbial mustard 

 seed to shame. As the late Professor 

 Brooks has rigorously demonstrated, one 

 of these microscopic organisms under fa- 

 vorable conditions is capable of filling the 

 ocean solid in less than a week, if all its 

 progeny were to live and keep on multi- 

 plying at the maximum rate during that 

 period. This is a stupendous fact and 

 it must be comprehended before one can 

 understand life in the sea. It explains 

 why such enormous communities of shell- 

 fish can be supported on a limited area 

 of the sea's floor. 



Unlimited food supply is coupled 

 with almost unlimited powers of repro- 

 duction. In the sea mussel we find the 

 strange condition in which practically 

 the whole body becomes a storehouse 



