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 

 earher.' 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 



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 



'All the linos of D. pulcx except 689 and 751 cnme from Pond II, the spring-fed pond in 

 the woods. 



