1919] Esterly: Reactions of Various Plankton Animals 27 



It is worth noting that in the tables dealing with the summary of 

 individual performances there are three items that indicate the kind 

 of response and the relative degree to which it is manifested: (1) 

 The relative number (expressed as percentages of the whole number 

 of animals) of individuals that move in the positive and negative direc- 

 tion. These numbers may be about equal, but either or both of the 

 following items will show more adequately the actual extent of posi- 

 tiveness or negativeness. (2) The proportion between the records that 

 show positive and those that show negative changes in position. For 

 instance, if an individual is recorded as moving toward the bottom 

 three times out of four and toward the top once it is good evidence 

 that it is a positively geotropic animal. (3) The distance traveled in 

 either direction is a very satisfactory index of the degree to which 

 one kind of reaction exceeds the other. If the figures giving the num- 

 ber of animals moving and those giving number of records should be 

 about the same in the positive and negative columns, while the figures 

 that show distance covered are very unequal (as between positive and 

 negative), I should be inclined to hold that the latter reveal the kind 

 of response given under the particular conditions of the experiment. 



The differences between the figures in the positive and negative 

 columns for each of the three items should always be compared when 

 considering the tabulated results. When the differences point in the 

 same direction in all three eases, the evidence is a good deal stronger 

 than if one difference indicates one thing and a second shows some- 

 thing else. 



It is desirable to note, in further explanation of the use of terms, 

 that "number of experiments" means the total number of times it 

 was attempted to ascertain the behavior of individuals under a given 

 set of conditions. The average number of trials given each animal 

 appears from the ratio between number of experiments and number of 

 animals tested. 



The table that follows (p. 29) contains the summary of the records 

 of individuals. The behavior under all intensities of light is included 

 in the summary, since the phototropism does not change with the 

 intensity as it does with the temperature. The extreme ranges of inten- 

 sity employed (as compared with the 15-watt lamp) were from 0.025 

 to 15,000 or more, with such intermediate intensities as 8, 196, 3800. 



The figures in the first line show that Calanus is strongly negative 

 to light. The range in temperature is that of the room at different 

 seasons of the year, and the salinity is that of sea water as it came 



