440 PI. S. JENNINGS AND K. S. LASHLEY 



whether the differences between the two members of the pairs 

 is less or greater than that between two strains taken at random. 

 For this purpose we will select the first twenty days of the experi- 

 ment (sum of the first two periods in table 51). There were 179 

 pairs (358 lines) that lived through this period. The average 

 difference in the number of fissions between the two members of 

 these 179 pairs, as determined by an examination of table 51, is 

 2.514 ± 0.122 fissions. 



The average difference between strains taken at random is 

 determined in the way set forth on page 424. Mating each of 

 the 358 strains with every other gives us 63,903 pairings; and the 

 average difference turns out to be 3.493 fissions. This is greater 

 than the average difference between the members of pairs by 

 1.429 fissions, or 56.8 per cent. 



Thus again we find that the average difference in fission rate 

 between members of pairs is not greater than that between strains 

 taken at random, as would be required in order to give evidence 

 of sexual differentiation; on the contrary it is very much less. 

 The progeny of members of pairs are more alike than are the pro- 

 geny of individuals that have not paired. 



We may now turn to an examination of this matter by the aid 

 of the coefficient of correlation. 



In table 45 are given the coefficients of correlation in number of 

 fissions between the two members, a and b, of the pairs, for the 

 various periods of table 51. It is important to recall again that 

 the coefficients for the longer periods (20 days, 40 days, etc.) give 

 evidence independent of that for the shorter periods (or at least 

 not bearing any simple and evident relation to the latter). 



As table 45 shows, the correlation in rate of fission between 

 the members of pairs does indeed show itself equally when we 

 experiment with very large numbers, and in such a manner as to 

 exclude the possibility that the similarity of the two members is 

 due to environmental similarity. In this experiment on 482 

 lines of propagation, as set forth in our description of methods, 

 the two members a and b, of a pair, are kept on separate slides, 

 in separate moist chambers, and handled separately — as a rule, 

 by different persons. All the experimental conditions are such 



