450 H. S. JENNINGS AND K. S. LASHLEY 



Comparative rate of reproduction in members of the split pairs 



The number of fissions for the progeny of the members of the 

 spht pairs was recorded for twenty days. We are here interested 

 in the question whether the two members of a split pair tend to be 

 ahke in their rate of reproduction, as is the case with the two 

 members of pairs that were not separated before conjugating. 

 For determining this, we have formed tables of correlation for the 

 number of fissions of each member a, as compared with its pros- 

 pective mate b. The results for the 190 split pairs during the first 

 ten days are given in table 46; during the second ten days (155 split 

 pairs) in table 47; during the entire twent}^ days (155 split pairs), 

 in table 48. These tables include only the lines in which both 

 members of the split pairs lived throughout the period in question. 

 The coefficient of correlation for such tables is found in accordance 

 with the method set forth on page 429. 



For the first ten days the coefficient of correlation for the 190 

 split pairs (table 46) is 0.1802 ± 0.0335. The correlation is 

 thus slight, but it may have some significance, since it is about 

 six time its probable error. 



For the second ten days (table 47) the coefficient is 0.0438 

 =t 0.0382, a result which, based as it is on 155 pairs (310 lines), 

 indicates that there is no correlation between the two members of 

 the split pairs. 



Finally, for the entire twenty days (table 48) the coefficient 

 of correlation for the 155 pairs is 0.2620 ± 0.0356. Here again 

 we have a small positive coefficient which comparison with its 

 probable error indicates to be significant. 



There appears thus to be a slight tendency for the prospective 

 members of a given pair to be a little more alike than usual, in 

 rate of fission, even before conjugation has occurred. That is, 

 there appears to be a slight degree of assortative mating with 

 respect to fission rate. This, if it actually exists, is doubtless 

 a secondary result of the assortative mating in size that is known 

 to occur (see Jennings '11). Possibly individuals of similar size 

 tend also to have a similar fission rate. 



But this ver}' slight pre-existing correlation, whose existence is 

 e\en doubtful, since it did not show itself in the second ten da3^s 



