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University of California Puhlications in Zoology [Yoh. 18 



Several methods have been employed (Michael, 1911; Esterly, 

 1912) for determining the relative distribution of a marine species 

 under different conditions. First, the direct method was used of 

 comparing the abundance or average number of individuals obtained 

 per unit volume of water filtered (= amount filtered per hour of 

 towing). Second, as the species would in general be present in a 

 greater proportion of those hauls made under the conditions when the 

 species occurred in greatest numbers than of those hauls made under 

 the conditions when it occurred in smallest numbers, the liaul fre- 

 quency, or percentage of hauls in which the species appeared under 

 one set of conditions, was compared with that under another set. It 

 is important that this be clearly visualized; perhaps an illustration 

 strictly analogous in principle although not in detail will make it 

 more intelligible. The President of the United States is elected not 

 by popular vote but by that of states. But, as a rule, the candidate 

 receiving the largest popular vote is elected. Suppose one wanted to 

 compare the Democratic preference of the nation during a period of 

 plenty with that during a period of famine. Assuming an equal popu- 

 lation in all states, could the investigator not proceed in two ways: 

 first, by comparing the average number of Democratic ballots cast per 

 state under the two conditions (=the abundance method) ; and second, 

 by comparing the proportion of states that went Democratic under the 

 two conditions (^the frequency method) ? If the first method indi- 

 cated a greater Democratic preference during the period of plenty, the 

 second method would, as a rule but not always, indicate the same thing. 



Finally, Esterly (1912, p. 282) compared the time frequency of the 

 species under one set of conditions with that under another, or to 

 quote: "the ratio between the time occupied by hauls in which the 

 species was taken and the total time spent in hauling. ' ' If the average 

 time consumed per haul were the same for hauls made under all com- 

 pared conditions, it is obvious that haul frequency and time frequency 

 would be identical. However, if ten hauls consuming ten hours were 



