62 



SELECTION IN CLADOCERA ON THE BASIS OF 



During the year (August 1912-July 1913) the means were 

 302.5 and 256.3 seconds. The difference (+46.2 ±12.1 seconds) is 

 3.81 times the probable error, a difference statistically significant. 

 For the 12 same-day broods the means are 314 and 254 seconds — 

 and the difference is +60 ± 21.68 seconds, 2.76 times the probable 

 error. 



Table 25. — Selection summary for Line 719. 



Table 26. — Same-day broods. Summary of data for Line 719. 



For the following year (August 1913-July 1914) the means are 

 409.6 and 366.3 seconds. The difference is +43.3 ±13.2 seconds 

 and is 3.28 times the probable error. Again the plus mean is larger 

 by a margin of statistical value. The 11 same-day broods have 



