JI-KGONY AND REVKKSION, 



121 



have desceiided from the blue rock pigeon {Columba livia), 

 and it has long been known that when distinct varieties of 

 pigeons are crossed^ the young sometimes very closely 

 resemble blue, rocks. Mr. Darwin refers to a pigeon 

 descended from a red spot and a white fantail on the one 

 side, and two black barbs on the other. This pigeon was 

 hardly distinguishable in its coloration from a wild rock 



pigeon. 



Darwin accounted for the occasional resen^blance 



of cross-bred pigeons to the rock pigeon, by saying they had 



Fig. 39. 



Sire of Hybrid shown in Fig. 37- 



undergone reversion. To quote from Weismann : " Darwin 

 was the first to point out that in cross-breeding, either of 

 species or of mere varieties, characters not infrequently 

 appear in the descendants which were not present in the 

 parents; in some of which cases, indeed, it can be 

 proved, and in others shown to be very probable, that they 



* ' Animals and Plants/ vol. ii, p. 14. 



