358 MISSES K. FOOT AND E. 0. STROBELL : RESULTS OF 



We seem compelled, therefore, to nssume that the female variolarius is 

 homozygous for the spot factors ; and if we assume that servns is without 

 them, then the Fj hybrids should be heterozygous for these factors. 

 Assuming that they are inhibited in the female, the males should all be alike, 

 either in having a variolarius spot or in having no spot. The facts, however, 

 are as follows : — Two of the eleven F^ hybrid males have no spot (photo 7), 

 and the remaining nine are variable intermediates (8 of the 9 are shown in 

 photos 8-14, and the 9th is a pinned specimen, which has a spot so small and 

 so faint that it is scarcely perceptible). 



An interesting case of F^ hybrids approximating a blend is the cross 

 between the pigmented silky hen and the unpigmented brown leghorn. 

 Prof. Punnett theoretically explains these intermediates (partly pigmented) 

 Fi fowls by the following assumptions : — 



1st. Assumes that the ? is heterozygous for femaleness (Ff). 

 2nd. Assumes that the c? is v.dthout this sex-factor (ff). 

 3rd. Assumes that the silky is homozygous for the pigment factor (PP). 

 4th. Assumes that the silky is without an inhibiting factor (ii). 

 5th. Assumes that the brown leghorn is without the pigment factor (pp). 

 Gth. Assumes that the brown leghorn is homozygous for an inhibiting 



factor (II). 

 7th. Assumes the inhibitor is sex-linked (there is a repulsion between 



I and F) . 



If we transfer all these assumptions to the variolarius x serous cross, even 

 to the extent of assuming that the female instead of the male is heterozygous 

 for the sex factor, they fail to account for the fact that these Fj hybrids 

 are not all intermediates.* Tioo are like sorvus m liaving no sjmt. Such 

 irregularities in the Fi generation are out of hnrmony with the 

 principle? of Mendelism, but in some forms similar evidence ag;iinst 

 Mendelism has been weakened, if not cancelled, by the fact that the F2 

 generation shows a regular Mendelian ratio. This is not the case, 

 however, with the F2 generation of the EuscMstus cross — of the 190 

 F. 2 male hybrids (photos 15-57), 19 have the spot quite as distinct a.'< that 

 of pure variolarius, 97 are very variable intermediates, and 74 are like servus 

 in having no spot. 



The classification of the Fg hybrids into these throe groups is based on 

 a study of the photographs, f and the numbers in each group were afterwards 



* It is obvious that in t)xQ females oi variolarius a special inhibitor must be assumed that 

 is outside the germ phxsm— for theoretically the spot appears in the female. 



t In classifying the photographs of the hybrids we included under the servus type not 

 only all those specimens with no spot whatever, but also those with merely a faint indication 

 of a spot, for tlie latter was not visible in the living specimens, and probably will not show 

 n the reproductions. 



