.1. K. 1)! KKDKN Ift.*) 



taiieouHly in nil the imli\ idualH. |)i*OHumubly it atVccli'd u W'w at Hrhl umi 

 otheni gnuiually. For a lon^ time in the history of th«« race noine of 

 the binis wouM be duplex for Imldness, some would be Miniplex and the 

 r(>8t would Ih' nulliplex. Mr (J. W. Manly (Punnttt's MendvUsm, IfUl, 

 \\ 136) haw shown that under eon<litions such lus are stipulate*! for the 

 tiatrich the jnipulation would rapidly fall into a stablr condition with 

 reganl to the pro|)ortion of the three forms, whatever may be tht* pn»- 

 portion to start with. If the |)opulation consists of p h(nnozy^ot<'s of 

 one kind, v homozy^tes of the othrr kind and Sry heterozygotes then 

 he points out that such a population would be in eipiilibriuni for a 

 particular fact-or so long as the condition (f = pr is fulfilled. The pro- 

 portions which satisfy the e(|uation are exceedingly numerous and in 

 case of any disturbance of the equilibrium, a.s by the app(;aranc<' (fe novo 

 of the charact<?r, it will be restored after a single generation. 



From the foregoing we gjither how little etTect undi'r natunil con- 

 ditions the importation of the hundred and thirty-two northern birds 

 would have upon the southern race if the population of the latter were 

 stationary. If all the northern birds reached breeding age and mated 

 with the southern they would in the end give rise to only double the 

 number of simplex, bald-headed ostriches, and the number would neither 

 increase nor decrease. How far the other characters — dimensions, colour 

 and nature of the egg — would influence the southern race cannot b<! 

 determined until their actual factorial values have been worked out. 



The conditions represented by the loss of scales from the middle toe 

 and the claw on the fourth toe further help in an understanding of how 

 mutative changes are introduced into a large assemblage. It is seen 

 that the loss of scales has occurred in individuals of both the northern 

 and southern birds, though more frequently in the former. The change 

 however must have appeared independently north and south, for the 

 distinctness of the other characters, especially that of baldness, proves 

 that no intermingling of the two species has taken place towards the 

 extremities of the continent. Appearing at first in comparatively few 

 individuals, and presumably in duplex dominant form, it is most unlikely 

 that a bird having the break would mate with another showing the same 

 loss, but rather with one in which the scutellation was continuous. The 

 duplex bird mating with a nulliplex would give F^ progeny in all of which 

 the break would appear, while germinally they would be simplex. The 

 simplex condition would tend to be retained until such time as the char- 

 acter became prevalent and opportunity occurred for a simplex to meet 

 with a simplex, when a duplex condition would arise. It is significant 



