28 SELECTION IN CLADOCERA ON THE BASIS OF 



ANALYSIS OF DATA. 



Line 695. 



Presentation of Data. 



The data for Line 695 may be considered first. Line 695 is one 

 of the original lines taken into the laboratory, the stock having been 

 obtained from the spring-fed pond in the woods (Pond II), November 

 17, 1911. The selection was begun March 26, 1912. The stock had 

 then descended 8 generations in the laboratory. By that time 

 methods of rearing and handling the material had been worked out 

 and the stock was well established. 



The manner of handling the young in making the selections has 

 already been discussed. The selection data complete, summarized 

 by broods, are given in the tables for the 695 plus and the 695 minus 

 strains. Tables 3 and 4 contain in successive vertical columns, 

 beginning at the left, the designation of the generation; the date of 

 selection from within the brood; the hour of the day at which the 

 experiment was conducted; the age of the young, whether a "new" 

 brood or a brood released a day earlier (Sunday's broods and rarely 

 others were tested when a day old); the number of individuals in 

 the brood; the temperature of the water in the experimental tank at 

 the time of the experiment; the number of individuals which went 

 to the negative end of the tank; the number of individuals which 

 failed to respond to the extent of reaching either end of the tank 

 within the period allotted (15 minutes); the minimum reaction-time 

 for an individual of each brood; the maximum reaction-time; the 

 sum of the individual reaction-times for the brood; the mean reaction- 

 time for the brood; and finally, the sum of the squares of the indi- 

 vidual reaction-times (for computation purposes). 1 



Consultation of tables 3 and 4 shows that there are wide differ- 

 ences in reactiveness of the various broods. These, in part at least, 

 are due to the factors discussed on pages 17-20 and 128-149 of this 

 paper. It is unfortunate, though not surprising, that these reaction 

 differences are so large, but when all of the factors of the case are 

 taken into account, it is believed that they are not unduly disturbing 

 to the course of the experiment. 



Because of the relatively wide differences in reaction-time be- 

 tween different broods and the small numbers in many of the broods, 



1 For the benefit of anyone wishing to go over the author's analysis or make further analysis, 

 it was desired to present the complete data for all the lines discussed in this paper. But (in view 

 of the present great cost of printing so many pages of tables) data are presented practically com- 

 plete for Lines 695 and 757 only. It is quite impracticable to publish the individual reaction- 

 times for all the individuals tested in making the selections, even for Lines 695 and 757. The sums 

 of the squares of these reaction-times are given. This renders available all the data necessary 

 for a critical analysis of the original data and should satisfy the most exacting reader, so far as 

 Lines 695 and 757 are concerned. The detailed data for all the lines have been typed in tabular 

 m, such as is used for the data for Lines 695 and 757, and are stored in duplicate at the Station 

 Experimental Evolution, where they may be freely consulted by anyone interested. 



