THE AMEBIC AN NATURALIST [Vol. LIII 



lost members had dropped out from the germ plasm, 

 especiallv if later breeding failed to restore them ; selec- 

 tion would have induced a definite change in the germ 

 plasm. Also if a pure line with 42 remiges were estab- 

 lished and no further increase occurred we should be 

 warranted in concluding that the factors for the plumes 

 beyond this number had already disappeared from the 

 race and could not be restored; the causative agent could 

 not act in a plus direction. It is unfortunate for such in- 

 vestigations that the ostrich is such a slow breeder. Ex- 

 periments are however being conducted to determine if 

 further reduction in the 33-plumed birds can be induced, 

 while the building up of a pure 42-plumed race is also in 

 progress, the latter having an important industrial bearing. 



In many respects the degeneration phenomena in the 

 ostrich appear to be best understood on the conception of 

 autonomous changes and variations in potency of the 

 germ factors. In the case of the dropping out of plumes 

 during the chick stage the reduction in potency has pro- 

 ceeded so far as to result in entire loss of effectiveness 

 only from the chick stage onwards, while complete loss 

 of factors from the germ plasm may be regarded as the 

 final loss of potency. May not a variation of potency of 

 factors be at the root of many of the so-called fluctuating 

 variations? The explanation seeks for the loss of factors 

 among the autonomous changes in the factors themselves, 

 while the idea of a causative agent" throws the respon- 

 sibility for the changes upon some influence external to 

 the factors. 



Since the above was written certain results have been 

 obtained which strongly support the idea that it may be 

 pos:^ibk' to induce retrogressive changes in the ostrich. 

 As <tattMl. a !.)>> of scales over the large middle toe has 

 already taken place in a small proportion. Out of twenty 

 southern birds of mixed breeding one showed a single 

 break while out of twenty mixed northern birds a single 

 break occurred in three cases and a double break in two. 

 The results given below are derived from the mating of a 



