130 Heredity. 



mother. As the possession of stripes is a characteristic 

 which distinguishes the zebra from the horse and the 

 ass, it seems at first as if its transmission by a female 

 ancestor is opposed to our theory. We know, however, 

 that all the species of the horse genus are the descend- 

 ants of a striped form, and the presence of stripes in the 

 zebra is not due to recent variation, but to the fact that 

 it has not varied. The transmission of stripes by a fe- 

 male zebra is therefore nothing more than we might ex- 

 pect. We know, too, that both the horse and the ass 

 show a tendency to revert to the striped ancestral form, 

 and I shall show in the next section that reversion is 

 often excited by crossing. It is therefore quite probable 

 that the stripes in this colt were due to reversion. 



It is said that young animals born from a tigress by a 

 male lion, as well as those born from a lioness by a male 

 tiger, are striped, but many cat-like animals show a ten- 

 dency to revert to a striped form, and in this case also 

 we may explain the presence of stripes in the young by 

 attributing it to reversion excited by crossing. 



Darwin says that a good authority assures him that 

 in South America, when niata cattle are crossed with 

 common cattle, though the niata is prepotent whether 

 males or females are used, the prepotency is strongest 

 through the female line. 



The origin of the niata breed is not known, but there 

 is no doubt that it originated in Paraguay from common 

 cattle; and the fact that the niata peculiarities are not 

 shared by any other living cattle, but are very much like 

 those of the extinct Sivatherium, seems to show that in 

 this case also the peculiarity is due to reversion. 



