314 



THE AMERICAN NATURALIST [Vol. XLVIII 



to high mortality, selection as might have been desired 

 has been impossible. 



A detailed account of this strain is given in Table II. 

 In recording any mating of this strain the letter c denot- 

 ing the entire strain, is followed by F 1? F 2 , etc., denoting 

 the generation from which the mated flies have been 

 chosen. This symbol is then followed by a, b, or c, denot- 

 ing the first, second, or third mating, respectively, of the 

 generation indicated. Thus mating c¥ 2 b is the second 

 mating of the second inbred generation of strain 1912 — c. 

 This method of recording matings has been followed 

 throughout my work. 



Several points of interest are to be noted in this strain 

 but it is thought best to present the remaining data on 

 reduced strains before proceeding to a discussion of this 

 matter. 



Strict inbreeding has been followed in the strain re- 

 corded below. In no case have there been either cousin- 

 matings or outcrossings. 



1913-4, L. sericata $ = 3, ac, ac, 3, taken at Bussey Institution, Forest 

 Hills, Mass., May 6, 1913, gave 



2<?<? = 3,ac, 3,: 

 2<?<? = 3, 3, ac, 

 1 c? = 3, 2, ac, 



erage individual of that generation. Because Dr. Pearl in his October 

 iper referred frequently to the paper by Dr. E. M. East ( '12) on "Hetero- 

 gosis in Evolution and Plant Breeding." I gave Dr. East my figure ex- 

 essing the per cent, of homozygosis in successive generations resulting 

 om matings of sisters with brothers. Dr. Pearl's correction followed a 

 tter from Dr. East which pointed out the error of applying the mathe- 

 nti.-s „f random matings in oa.-h generation to a case where sisters always 



shed by Dr. Pearl for tlio following generations: P.- Kill per cent., F, — 

 ir cent., F 2 — 50 per cent., F 3 — 50 per cent., F— 62.5 per cent., Fc — 68.25 

 >r cent., F,— 75 per cent., Fr— 79.687 per cent., F 8 — 83.594 per cent, F — 

 1.719 per cent., F,„— 89.258 per cent. Previous to giving these figures to 



