188 Grossing the North and South Africa}} Ostrich 



still further degree. As already indicated, the numerous " points " in 

 the feather to which the farmer attaches importance behave in breeding 

 practice as if each were under separate control. On the other hand we 

 have abundant evidence that in ordinary breeding, and also in degenera- 

 tion, each plume usually acts as an independent whole, as if some factor 

 or group of factors controlled it in its entirety, irrespective of its 

 numerous component factors. A complexity is however introduced by 

 the presence of vestigial, imperfectly formed feathers, a few of which 

 are sometimes found beyond the last fully developed plume in a row, 

 and also as vestigial down on the wings and tail. Where vestiges occur 

 during degeneration we can only surmise that the factors which control 

 the whole plume may drop out piecemeal. They show that meristic 

 structures do not always appear or disappear in their entirety. We 

 may have a part of a feather as well as a whole. 



Among the mixed assemblage of ostriches of the present day the 

 genetic factors controlling the number of wing plumes in each bird may 

 be regarded as heterozygous, for from any pairing we get a fluctuating 

 series around some mode, less wide in some cases than in others ; but if, 

 as seems likely, it is found possible to extract pure lines for each of the 

 numbers from 42 to 33 these will then breed true and may be expected 

 to be homozygous. 



The loss of scales from the middle toe evidently represents a germinal 

 change which is actually in progress in both northern and southern birds 

 at the present time. It proceeds along parallel lines in both races, its 

 first manifestation being a loss of scales at the joint between the tarsus 

 and toe and then another over the middle of the toe. The breaks re- 

 present a loss of structural parts of the foot, though they are dominant 

 over continuity. As yet- the germinal change involved in the first break 

 has affected only a small proportion of birds and the second break a still 

 smaller proportion. The other facts of degeneration in connection with 

 the foot, the claw and scales over the small toe, and the loss of three toes, 

 are taken to justify the assumption that the breaks represent still further 

 degeneration which is in progress for the ostrich race as a whole. If, 

 when first introduced, the change is a homozygous one, there is small 

 likelihood that, in mating, the homozygote will meet with another homo- 

 zygote. Until the mutation is introduced among a considerable number 

 of birds the chances are that pairing will take place with a nulliplex 

 individual, in which case all the progeny will be heterozygotes ; these 

 in turn are more likely to pair with a nulliplex, and as regards the break 

 the offspring will be simplex dominant and nulliplex in equal numbers. 



