CROSSING AND ATAVISM 



19 



ewes of the various mountain ,,breeds to produce feeding 

 sheep. 



The first cross between two breeds is, in character, 

 usually intermediate between them ; but after the first cross 

 it cannot be predetermined how the tendency may run. The 

 first cross is the strongest : after-crosses get smaller and 

 weaker, and the more so the longer crossing is continued, 

 especially if close-breeding be practised, necessitating the 

 going back now and then to one of the pure breeds for a sire 

 to infuse new vigour. This so far explains the success of 

 crossing mongrel cows with a pure Shorthorn bull. 



Atavism (from atavus, an ancestor), or " throwing back," 



JB 



FIG. 1. Cross-bred Cow, showing reversion in colour to that of the ancient wild cattle : 

 Drawn by Mrs Blackburn. 



or " reversion," is the appearance in an animal of some 

 character which the immediate parents had not, but which 

 existed in its ancestors. A striking instance, for example, was 

 reported to the Author by Professor Blackburn in 1893 ' 



" About thirty years ago Mrs Blackburn got, at Roshven, 

 Moidart, N.B., a pure Brittany bull and cow, but after some 

 years there was a difficulty in securing a pure Brittany bull 

 to keep up the stock, and a young bull a cross between a 

 Brittany and a Shetland was bought. A very considerable 

 proportion of the progeny of this bull by the pure Brittany 

 cows were pure white, with black ears and points like the 

 wild white cattle not albinos." 



