J., E. DrKKDKN H)9 



the gnuiuiil IninHition, while the nuMlium tiitt nuiy or nuiy imt ]N>rHiHt. 

 No ei)rn\M|M)mIiiig falling out of thf fcjithcTH cvrr (nkrs place in the 

 Capt» chick. 



Nfttunilly JH^me interest ha« Ix'rn attii(h«<l U* thr Ixhaviour of the 

 Iwild |)iitch in th<» cn^sscs of (he northern and southern ostrich. Of the 

 humlriHl or so cn)ss-hnMl chicks which have hwu hatched none iit first 

 showed any signs of Iwildness, hnt in every case the f<'athers iM'gan to 

 fall out when the chick was two «»r three months old, and at six months 

 the [Mitch was established as completely jis in adult N«>rth African 

 i»striches. Thus the baldness of the northern bird is shown to be 

 dominant over its absence in the southern bird. 



The two second i^eneration chicks already reared are now w<'ll nvei- 

 the age at which the bald patch becomes established, and in one of thr-iii 

 the head remains coveri'd with hairy feathers jis in southern binls while 

 in the other the baldness h;is been formed ixs distinctly us in any 

 northern bird. The F.^ chicks thus atibrd evidence that factorial segre- 

 gation tjikes place in the second hybrid generation, and there can be 

 little question that when sufficient chicks of this generation have been 

 obtained it will be found that baldness behaves as ;i homozygous dominant 

 in strictly Mendel ian proportions. 



The bald head piitch is therefore a distinctive Mendelian unit- 

 charactvr sepjvrating the northern and the southern ostrich. The 

 differences jissociated with the dimensions and colours of the birds, and 

 also those of the agg, are differences of features common to b(jth, but in 

 the Cape bird there is nothing suggestive of the baldness of the Nigerian. 

 It is an entirely new character which has appeared in the latter race of 

 ostriches, but not in the former. It may be regarded as a mutation, 

 and was presumably fully developed from the beginning, for though it 

 varies somewhat in its extent and form the differences are no more than 

 can be regarded as fluctuating variations. That it is germinal in its 

 origin is manifest since it appears in all chicks, both pure and cross-l)red, 

 while its dominance in all the latter proves that the parents are du|)lex 

 or homozygous with regard to it. 



It Ciin hardly be suppo.sed that the baldness h;is arisen in response to 

 any external influi-nce, for it is unlikely that anything environmental 

 could affect the top of the head of the northern bird which w(»u]d not 

 have a corresponding action upon its southern relative, even if it were 

 possible that any influencing of the kind could bring al)out a corre- 

 s}x»nding change in the germ phusm. Nor can it be deemed to have any 

 adaptive value. It lends strong support to the view maintained by 



