46 



SELECTION IN CLADOCERA ON THE BASIS OF 



LINE 689. 



Line 689 was obtained from the surface-water pond in an open 

 field (Pond I) and reared in the laboratory for 8 generations before 

 being subjected to selection. Selection was continued 16 months, 

 44 generations in the plus strain and 42 generations in the minus 

 strain, when the experiment was terminated by the accidental loss 

 of the plus strain. 



The data are presented after the plan followed with the data 

 for Line 695 in tables 9, 10, 11, and 12, and in figure 3, A, B, and c. 



For the first 4 months of selection the mean reaction-time for 

 the plus strain was 498.4 seconds and for the minus strains 464.2 

 seconds. The difference was +34. 2 41. 4 seconds (table 11). 

 For the year (nearly), from August 1, 1912, to the close of the ex- 



TABLE 9. Selection data summarized by two-month periods for Line 689 plus. 



Time period. 



Apr.-May 1912.... 

 June-July 1912... . 

 Aug.-Sept. 1912. .. 

 Oct.-Nov. 1912. . . 

 Dec. 1912-Jan. 1913 

 Feb.-Mar. 1913.. 

 Apr.-May 1913... 

 June-July 1913... 



10-14 

 15-19 

 20-23 

 24-26 

 27-33 

 34-40 

 41-47 

 48-52 



11.1 

 9.0 

 17.8 

 18.7 

 9.0 

 8.3 

 7.9 

 8.2 



0.48 

 .58 

 .13 



ll 



r = 



TABLE 10. Selection data summarized by two-month periods for Line 689 minus. 



