18 A TREATISE ON HORSE-BREEDING. 



climatic influences and artificial selection and 

 crossing, is generally admitted by naturalists. 



It is one of the principles of heredity, that 

 when there is a great uniformity in a species 

 divergences from the usual type in the off- 

 spring are slight and rare; but when this uni- 

 formity, from no matter what cause, has been 

 broken up, divergences in the offspring are 

 frequent and great, although there is always 

 present a tendency, more or less powerful, to 

 revert to the original type. This tendency is 

 most frequently manifested when breeds or 

 races, widely differing in their present forms, 

 are crossed upon each other. In such cases, or 

 violent crosses as they are called, it frequently 

 happens that the progeny resembles neither 

 parent, but shows strong marks of the type 

 from which both of its ancestors originally 

 sprung. Darwin gives numerous illustrations 

 of this tendency to reversion in his experi- 

 ments with pigeons of various breeds and col- 

 ors, one of which I quote, as follows: 



I paired 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 throw- 

 ing any other color. Nevertheless, the offspring from the 

 above two mongrels were of exactly the same blue tint as 

 that of the wild rock pigeon, from the Shetland Islands, over 



