J. K. DrKHDKN 1H7 



representation in the ^riu phutni. Thr \mU\ {rntch Ih a tin it chanicter 

 which htis appeannl in the northern without any c'orreH|x)n(lin^ chan^i* 

 in the mmthem binl. In all the individualH nmKi for erosHin^ it iK'haveh 

 in a honn»zygi>us numner, showing that it haw iH'conie fully cMtabliMhe*! 

 throughout the northern nice. It Hupj)ortH the pri*Menc<! and absmci- 

 ooaoeption of genetic factors ; the factor for baldness is present in duplex 

 form in the genu cells of the northern ostrich but is absent from thosr 

 of the southern. In cross-breds of the finjt generation it is simplex 

 dominant, and in cross-breds of the second generation it is found to 

 segregate. 



The dimensions and colonics of the ostrich, a,s well jis the varic^us 

 features of the egg, have manifestly a more complex fact<jrial representa- 

 tion than the bald p<itch. In the ancestral ostrich the factors for each 

 of the characters were doubtless common to all the individuals, but 

 germinal divergence has since taken place. The cross-breds serve to 

 establish that each species now has its own separate factor or factors 

 controlling its size, for those of the one are neither dominant nor re- 

 cessive to those of the other. They do not constitute an alternative 

 pair, a presence and an absence, as in the wise of the bald piitch. Hence 

 in the zygote resulting from the cross-mating the simplex factors for 

 both races are represented, the factor for the small size of the southern 

 bird and that for the large size of the northern. In the resulting soma 

 the two sets of forces are, as it were, each independently striving for 

 expression, and naturally the individual cannot be both sizes at the 

 same time, but appears a.s an intermediate, a resultant of the interaction 

 of two distinct tendencies, one from the northern parent and one from 

 the southern. 



Similarly with the body colours. Each species may be deemed to 

 have its own distinctive factors controlling its colours, for in crosses they 

 do not behave as alternative pairs. In the cross-bred bird each factor 

 endeavours to exert its pure specific influence, the result being a com- 

 bination of the two, a cohjur which is intermediate and partakes of the 

 nature of both ; sometimes one factor may gain a slight ascendency and 

 sometimes another. The same conclusions as to factorial distinctness 

 have been arrived at with regard to the various characters of the eggs 

 which appear as intenuediates in the F, crosses. The exact gametic 

 constitution, as regards the dimensions, coloui-s, and eggs, can however 

 be determined only after a number of chicks of the second generation 

 have been reared. 



The factorial representiition fnr the plumes must b«- complex to a 



Journ. of Gen. vui 18 



