Abstract
Through the methods of S. N. HAZEL (1943), I made the selection index of F2 poputation on three characters, Iength of cocoon filament (m. X1), weight of cocoon filament ( cg, X2) and width of cocoon (1/10mm, X3), of silkworms. Also I, calculated heritabilities and genic correlation by the way. Heritabilites and genic correlations were gained by means of F2 population and back-cros;s populations and their values are given in table 3. The selection index with three characters represented by units in brackets will be given as f emale I = 22X1 + 852X2 + 42X3 male I = 66X1 - 854X2 - 154X3 if breeding purpose is H=G1+G2 where X2 is a phenotypic value. G1 is a additive genic value and H is the genic value of their composite characters. In the real case, I think that we can carry F2 to F3 by random mating, after excluding inferior in dividuals of F2 population by these indexes. Besides, these three characters are not meaningful particularly, and what is breeding purpose, is another pr.oblem.
