48 A TREATISE ON HORSE-BREEDING. 



the only exceptions being that of Ptolemy II 

 with his niece, from which was produced Pto- 

 lemy III, and Ptolemy YII with his niece, the 

 produce being Ptolemy VIII, the grandfather 

 of Cleopatra, the descent in all other cases pass- 

 ing through wives that were not nearly related 

 to this family.* 



The testimony of experienced naturalists and 

 of intelligent and careful observers among prac- 

 tical breeders is uniformly in favor of the prop- 

 osition that a cross in the blood gives increased 

 size and vigor to the produce. It is an equally 

 well-established fact that cross-breeding, or the 

 pairing of animals of distinct varieties, usually 

 results in increased fertility; but it is rather 

 singular that, while this result usually attends 

 the pairing of distinct varieties of the same 

 species, yet if cross-breeding be carried so far 

 as to unite distinct species, although increased 

 size and vigor are still attained, fertility is 

 almost entirely lost. A familiar illustration is 

 seen in the produce of the horse and the ass. 

 The mule, resulting from such a union, is often 

 larger than either parent, and is noted for his 

 hardiness and powers of endurance, but the 

 power of reproduction is in nearly all cases 

 totally wanting. The same is true of most 

 other hybrids. It is a singular fact that a loss 

 of fertility is also one among the very first bad 



*" Hereditary Genius," by Francis Galton, p. 152. 



