FACTS OP INHERITANCE 147 



(5) Reversion. — Another mode of inheritance 

 — ^known as Reversion — is seen when the offspring 

 exhibits features which were not expressed in its 

 immediate ancestry, but were characteristic of 

 more remote ancestry, as when crossing different 

 races of pigeons, which have been breeding true, 

 results in the production of the ancestral rock- 

 dove type. Professor Cossart Ewart crossed an 

 " Owl " with an " Archangel " and obtained a 

 hybrid more like the former than the latter. He 

 crossed this with a prepotent white fantail and 

 obtained two pigeons closely resembling the wild 

 rock-dove type. Darwin laid stress on such 

 reversionary Blue Rocks which occur when widely 

 differing breeds are crossed and the hybrids are 

 bred together, but some recent experiments, e.g. 

 those of Staples-Browne, suggest that there may 

 be a Mendelian interpretation even of Darwin's 

 classic cases of reversion. The case of rabbits is 

 very suggestive. When rabbits of different colours 

 are turned loose and breed together, their descend- 

 ants tend to be eventually all grey, Darwin 

 regarded this as a reversion, and it may still be 

 described as reversionary; but it is not due to 

 the reassertion of long latent grey colouring. The 

 return to grey is due, as the Mendelian experiments 

 show, to the recombination of at least eight 

 colour-ingredients that go to the make-up of 

 wild greyness. Man has sifted out all the various 

 colours from the complex coloration of the wild 

 stock, and when the long-separated items are 

 brought together again by unrestricted inter- 

 breeding there is, naturally enough, a reconstruction 

 of the original grey colour. 



(6) New Departures. — Just as we began by 



