180 Crossing the North and South African Ostrich 



is doubtful, seeing that the factors for any higher number have probably 

 been altogether lost to the race, even if they were ever present in the 

 ancestral ostrich. 



Table VIII shows that when the 42-plumed southern cock is mated 

 with various North African hens of the 36 strain the average number 

 of plumes in the progeny is practically intermediate, namely 39*56, the 

 lowest number being 37 and the highest 42 ; they do not regress to the 

 general average. The numbers form an approximately normal curve 

 with the mode at 40. None of the birds hitherto employed as breeders 

 can be deemed " pure " as regards the number of plumes ; and the 42- 

 plumed bird is probably heterozygous like the rest ; hence the fluctuating 

 series represented below. 



TABLE VIII. 



Number of first-row Plumes on Cross-bred Chicks from mating a 

 4r'2-plumed Southern cock and 3Q-plumed Northern hens. 



Experiments are being undertaken to determine how far it is possible 

 to extract numerically pure lines, especially as regards the two extremes 

 33 and 42, but progress is necessarily slow. Until this has been done 

 full proof will be lacking that each plume has its own factorial repre- 

 sentation, though all the evidence points in this direction. 



The 33-plumed birds represent the extreme of the loss of wing quills 

 which has taken place in the ostrich of to-day compared with the maxi- 

 mum of 42 plumes. If, as we seem bound to suppose, some intrinsic 

 influence is at work within the germ plasm inducing slow retrogressive 

 changes, it appears not unlikely that by in-breeding pure 33-plumed birds 

 it will be possible to increase the action of the degenerative force and 

 produce a still further loss of plumes. By selection it should be possible 

 to control the further evolution of the ostrich with regard to the number 

 of its plumes. 



