I/O THE DOCTRINE OF DESCENT. 



are races of pigeons purely bred for several centuries, 

 and in colour and shape transformed into new creatures, 

 which yet from time to time spontaneously, or by 

 crossing with other conspicuous races, produce birds 

 which, in colouring and characteristic pencilings of 

 black bars on wings and tail, resemble the wild rock- 

 pigeon. 



" I paired," says Darwin,*^ " a mongrel female 

 barb-fantail with a mongrel male barb-spot, neither 

 of which mongrels had the least blue about them. 

 Let it be remembered that blue barbs are excessively 

 rare ; that spots, as has been already stated, were 

 perfectly characterized in the year 1676, and breed 

 perfectly true ; this likewise is the case with white 

 fantails, so much so that I have never heard of white 

 fantails showing any other colour. Nevertheless, the 

 offspring from the above two mongrels was of exactly 

 the same blue tint over the whole back and wings as 

 that of the wild rock-pigeon of the Shetland Islands ; 

 the double black wing-bars were equally conspicuous ; 

 the tail was exactly alike in all its characters, and the 

 croup was pure white." 



Another reversion frequently to be observed is the 

 striping of the feral domestic cat of Europe, in which 

 it resembles the wild-cat so closely as to be scarcely 

 distinguishable. Darwin has collected evidence from 

 which we may infer that the wild ancestral stock of 

 the horse was striped, and this evidence includes the 

 appearance of striped individuals. But yet another 

 strange phenomenon in horses may be interpreted by 

 atavism. Foals are occasionally born with supernumerary 

 toes. This " monstrosity " can be explained only by 



