MENDELISM AND WEISMANNISM 373 



either case, if the hybrids are inbred, it will reappear in pure 

 form in the next generation (F^), and so forth. There is, how- 

 ever, no warrant for the common belief that hj^bridisation in 

 itself gives rise to new races. 



Mendelism and Weismannism. — Mendel's discoveries lead us 

 to regard the inheritance as built up of " items/' which may be 

 inherited independently — e.g. unit characters corresponding to 

 the '' unit characters " of the organism, tallness, dwarf ness, yellow 

 albumen, green albumen, purple colour of flowers, white colour 

 of flowers, and so on. These correspond to Weismann's primary 

 constituents or determinants — the germinal representatives of 

 the independently heritable and independently variable characters 

 of the organism. 



In crossing grey and albino rabbits, Mr. C. C. Hurst obtained 

 in the F- families, cases of three grey : one albino ; and cases of 

 nine grey : three black : four albino ; in either case, according 

 to the Mendelian rule, three coloured : one albino. 



" The albinos can give no more coloured. The blacks may be 

 pure blacks, or they may give blacks and albinos. The greys may 

 be pure greys ; or they may give greys and albinos ; or greys and 

 blacks : or greys, blacks, and albinos, as before. 



" Of the four albinos, for instance, which appear on an average 

 in 16 F-, one will be carrying the grey determiner, one the black 

 determiner, and two will have both grey and black determiners. 

 By suitable cross-matings the condition of each albino can be 

 exactly determined. For example, when bred to a pure black, a 

 G albino will give greys only ; a G B albino will give equal numbers 

 of greys and blacks ; while a B albino will give blacks only. Simi- 

 larly, the exact composition of each coloured rabbit may be deter- 

 mined by experimental breeding. 



" The particular colour of a rabbit or mouse is therefore not a 

 simple character depending on the presence of a single factor, but a 

 double one, depending on interaction between one factor and another 

 each factor being transmitted independently in heredity." 



It seems to us that these complexities land us in close 

 approximation to the concept of germinal selection. 



