38 On Inlien'tance of \Vei)/Jit in Fotiltn/ 



larger F, birds the results coukl be expressed in the form of a biuiodal 

 curve whereas a uniiiiodal curve was given by the sniallei- F., birds. 

 These results are readily explained i>n the hypothesis we have just 



outlined. The gametes produced by an F, bird are of 16 sorts, viz. 

 ABCD, ABCd, ABcD, ABcd, AbCD. AbCd, AbcD, Abed, aBCD, 

 aBCd, aBcD, aBcd, abCD, abCd, abcD, abed. With abed gaimtes 

 such a series would give rise to the giades 226, 201(2), 176, 188(2), 

 163(4), 138(2), 150, 125(2), 100. These grades as .shown graphically 

 in Fig. 3 give rise to a bimodal curve in which the greater mass is 

 collected on the upper mode. It is the form of curve which we 

 should expect when Fi or similarly constituted birds are crossed with 

 some mufurm strain. It is the form of curve which was actually 

 obtained when F^ (and similar F.,) birds were ero.ssed with the pure 

 Brown Leghorn (cf Fig. 2, p. 32). Tlic' rcsulls nftci- an interesting 

 corriiburation of our views as U> I lit- ii.it iiii' of tin- F, birds frniii the 

 Sebright-Hamburgh cross. 



In connection with nur iiiti-rpii'taliiiii we may call attention to tiie 

 following point of theoretical, and possibly also of practical interest. 

 On our hypothesis two strains of intermediate and similar weight are 

 possible, viz. AAbbCCdd and aaBBceDD. A cross between two such 

 strains would I'esult in F^ biids rather larger than either, while the F., 

 generation would be like that shown in Table II. In other words a 

 cross between two medium sized strains of the same average size may 

 lead in F., to the production of strains considerably lai-ger and also con- 

 sideiably smaller than either of the parent strains, both of which can be 

 readily fixed. It is possible that the great size of many Horal varieties, 

 e cr. in daffodils, has been effected on these lines from crosses between 

 medium sized forms differing in constitution for the factors affecting 

 size. It is not impossible that the increase sometimes observed on 



