262 SOME RESULTS OF OSTRICH INVESTIGATIONS. 



The bald patch is therefore a distinctive Mendehan unit- 

 character, separating the northern and the southern ostrich. The 

 differences associated with the dimensions and colours of the 

 birds, and also those of the egg, are dift'erences of features common 

 to both, but in the Cape bird there is nothing suggestive of the 

 baldness of the Nigerian. It is an absolutely 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 jiresumably fully deve- 

 loped 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 jnire and 

 cross-bred, while its dominance in all the latter proves that the 

 parents are duple.x or homozygous with regard to it. 



It can hardly be supposed that the baldness has arisen in 

 response to any external influence, for it is unlikely that anything 

 environmental could affect the top of the head of the northern 

 bird which would not have a corresponding action upon its 

 southern relative, even if it were possible that any influence of 

 the kind could bring about a corresponding change in the germ 

 plasm. Nor can it be considered as having any adaptive value. 

 It lends strong support to the view maintained by Prof. W. 

 Bateson and also by Prof. T. H. Morgan, that new characters 

 make their appearance as a result of changes in the germ plasm 

 without any reference to external influences or any utilitarian 

 value or need of the individual. Since the baldness is now 

 ]jresent as a duplex dominant in all the imported birds, it must 

 have originated long ago in the history of the northern ostrich, 

 sufiiciently long for the change to have aff'ected all the individuals. 

 For, as wall be shown later, there is good reason to suppose that 

 in the ostrich a new character appears at first in only a few 

 members, but gradually extends to more and more, by the 

 continued change de novo in the germ plasm of the nulliplex 

 members of the race. 



The Egg. 



As in all other birds, the eggs from the same ostrich and als!^ 

 from different ostriches vary within certain limits, are regards size, 

 shape, and surface characters. Beyond these fluctuating varia- 

 tions, however certain well defined differences distinguish the q^^ 

 of the North African from that of the South African bird. 

 (PI. 4A.) 



Egg of North African OstricJi. — The eg;^; of the northern 

 bird is practically always larger than that of the southern, the 

 shell is almost free from obvious pores or pittings. and presents 

 an ivory-like smooth surface. Usually also the northern egg is 

 rounded in shape and less oval. Measurements have been taken 

 at the nest of the long and short diameters of four series of eggs, 

 and the averages are as follows : — 



