2o6 BULLETIN OF THE BUREAU OF FISHERIES. 



in the stomach of one of these scup were found copepods, while in the alimentary tract of these last one 

 could identify one or two of the diatoms and an infusorian test among the mass of triturated material 

 which formed its food. This is an instance of the universal rule of this kind of food: The squeteague 

 captures the butterfish or squid, which in turn have fed on young fish, which in their turn have fed 

 upon the more minute Crustacea, which finally utilize a microscopic food supply. 



These microscopic organisms constitute an unfailing, ultimate food supply and, 

 without it, the larger animals of the ocean, whose chief business is to devour each other, 

 would soon exterminate themselves. It consists of single-celled plants and animals, 

 chief among which are the diatoms and radiolarians. According to Peck these two 

 groups alone may be regarded as the great primary food supply for the larger marine 

 animals. The diatoms, in particular, may be said to constitute the pastures of the sea. 



How these minute organisms can support such a large and extensive fauna may be 

 readily understood when their habits are known. In the first place they exist in the ocean 

 in countless myriads. Brandt (1902) describes a haul made in Kiel Bay with a net 

 having a mouth area of 0.1 square meter which was lowered down to a depth of 20 

 meters and then hauled up. It was found to contain 3,173,000,000 diatoms, 500,000 

 peridinians, and 15,000 copepods. He estimated that this represented not more than 

 one-third the total number of organisms in the column of water, owing to the escape of 

 the smaller and more abundant species through the pores of the net and the fact that 

 all the water entering the net did not pass out through the pores of the silk. According 

 to his calculation the number of diatoms per liter would be about 6,000,000. Kiel Bay 

 is particularly rich in plankton organisms, so these observations may be taken to repre- 

 sent a maximum value. For a minimum value we may take the observations of Lohman 

 (1903), who examined the water of the Mediterranean Sea off Syracuse, which is poor in 

 plankton. He found that 1 cubic meter of the water contained 2,082,740 Protophyta, 

 325,510 Protozoa, 17,415 Metazoa, 785,000,000 bacteria. Moore (1907) made careful 

 measurements of the number of diatoms in the waters of Matagorda Bay, Tex., and 

 found from 13,250 to 70,500 to the liter. The west Baltic was found by Hensen to 

 contain about 457,000 diatoms per liter at the time of maximum abundance, and accord- 

 ing to Johnstone (1908) the number of diatoms that inhabit the North Sea or the Baltic 

 beneath every square meter of surface is between one and four millions. It is evident, 

 therefore, that they represent the most abundant organisms in the sea, numbering 

 anywhere from thousands to millions per liter of water. They occur in all parts of the 

 world and are more abundant in the temperate than in the tropical seas. They appear 

 in maximum numbers in the spring and fall of the year. 



In structure a diatom is a minute, single-celled plant surrounded by a cell wall of 

 cellulose and inclosed in a flinty case which is often most elaborately sculptured. Pelagic 

 forms have thinner shells, and the characteristic ornamentations are less prominent. 

 Some possess organs for suspension, such as buoying vesicles, enlarged flattened surfaces, 

 projecting hairs, lamelliform outgrowths, or secretion of mucilaginous filaments. The 

 outside case is always made up of two valves, one of which fits over the other like the 

 cover of a pill box. The interior of the cell is filled with cytoplasm containing a nucleus 

 usually located in the center. Colored bodies, called chromatophores, are present in 

 the cytoplasmic contents, often as two large plates which lie parallel and extend nearly 

 the whole length of the cell, or as numerous, small, oval bodies like those common in 

 the higher plants. They contain chlorophyl, but the green color is disguised by the 



