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. 



Time period. 



Nov. 13, 1912- 



July 31, 1913 

 Aug. 1, 1913- 



Junel 1,1914 

 Test series 



Jan. 1914 

 Dec. 1, 1913- 



Feb. 28, 1914 



Strain. 



Plus. 

 Minus . . 



Plus 



Minus . . 

 Plus.... 

 Minus . . 

 Plus. ... 

 Mimu.. 



1-31 

 1-31 

 32-71 



32-70 

 54 

 63 



48-58 

 47-67 



El 



282.2 

 70.8 

 375.4 

 400.7 

 416.1 

 433.9 

 414.0 



179.6 



164- 1 

 252.7 

 56.7 

 260.0 

 67. 7 

 233.0 

 S5K.6 



fe 



i 



Is 



7.73 +11.4 

 6.78 

 9.51 

 9.62 

 9.7 

 10.0 



-74.7 



10.28 1.10 



IS. 46 1.88 



IS. 9 



i.es 



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. 



Minus.. 



325 



170.04 



II 



+37 



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

 the woods. 



