66 



SELECTION IN CLADOCERA ON THE BASIS OF 



LINE 751. 



Line 751 was obtained in October 1912 from the surface-water 

 pond on the upland (Pond I), from which Line 689 came a year 

 earlier. 1 Selection was begun at once. This is the only line of Daph- 

 nia pulex with which selection was not begun during March 1912, 

 after having been in the laboratory from 5 to 8 generations before 



TABLE 27. Selection summary for Line 751. 



TABLE 28. Same-day broods. Summary of data for Line 751. 



Time period. 



Nov. 13, 1912- 

 July 31, 1913 



Aug. 1, 1913- 

 June 11, 1914 



Strain. 



Plus.... 

 Minus . . 

 Plus.... 



Minus . . 



7.4 



U 



119 



136 



88 



ni 



N 

 II 



I! 



00 J3 



K 



Avera 

 time. 



166 

 165 

 165 

 10S 



Aver 

 tim 



489 

 475 

 565 

 676 



325 



55 

 350 



204.06 

 170.04 



12.62 



II 



1l 



ll 

 Q ft 



+37 



+5 



ble 



16.022.30 



the beginning of selection. Selection was continued for almost 20 

 months, when both strains were lost (in the seventy-first and seven- 

 tieth generations). The data for this line are given in tables 27 and 

 28 and figure 9. 



For the first longer period of selection (9 months) the mean 

 reaction-time for the plus strain was 282.2 seconds, for the minus 

 strain 270.8 seconds. The difference (+11.4 10.28) was not 

 significant (table 27). There was a large number (16) of same-day 



1 All the lines of D. pulex except 689 and 751 came from Pond II, the spring-fed pond in 

 the woods. 



