Permanence and Evolution. 65 



than twelve generations, and of these birds, 

 " though highly valued by fanciers," being so 

 recently crossed with the rock dove, or rather, 

 perhaps, with similarly marked sub-strains of 

 their own breed, when evidently we want to 

 know all about the history of the particular 

 strains, and the views of the owners through 

 whose hands they had passed ; besides that, in 

 what is said about reversion, there is a confusion 

 between a cross diminishing at each generation, 

 as when a black barb, one of whose parents is 

 white, is paired with a black one of pure pedi- 

 gree, and a cross not diminishing, as when two 

 black barbs are paired, both of whom had one 

 parent white.* 



The rock dove, in its three various sub- 

 races, is the common pigeon of all parts of the 

 world, and therefore likely to cross the fancy 

 breeds accidentally. It is also the handsomest 



* It is also quite possible that the domestic' races of pigeon are 

 crosses between the rock dove and certain extinct types, the 

 rock dove being one element in every breed. 



F 



