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Isabel McCracken. 



similars of random selection, second bred from similars of pure 

 selection) certain broods were chosen from those designated in 

 Table II, for B X B crossings, and in Table III, from broods true to 

 parents for S X S crossings. Males of one brood were allowed 

 to breed freely with females of another brood as in previous 

 experiments. Great mortality prevailed at this time, materially 

 affecting the number of S broods available. Tables IV and V 

 show results in the aggregate. 



Table IV shows no reappearance of S in the fourth generation 

 from B X B. 



Table V— SxS. 



The results in Table V while involving but four parental broods 

 are consistent throughout, making it probable that B can be elimi- 

 nated from the S X S line in three generations of selective mating. 

 Whether it would reappear later must be determined by future 

 experiment. 



The accompanying diagrams represent the ancestry of two 

 third generation broods. The numbers used are the recorded 

 numbers of certain individuals in Table I, and certain broods in 

 other tables. 



Fig. I shows that all the offspring reared through the third 

 generation from the eight great-grandparents; that is, from 19 c^, 

 19 9, 27 c?, 27 9, 39 c?, 39 9 and 29 6", 29. 9 are B, and this 



