FARM ANIMALS 23 



this matter has been tested very thoroughly by Prof. 

 Ewart in breeding hybrids between zebras and the 

 horse. His long-continued and careful experiments 

 have shown as conclusively as may be that the theo- 

 ry of the influence of a previous sire must be entirely 

 discarded. 



In the various systems of breeding different meth- 

 ods have been used. In the origination of pure 

 breeds it has often been found necessary to use in- 

 and-in breeding. This term signifies the use of 

 animals of close relation as for example where broth- 

 er and sister and father and offspring are crossed. 

 The purpose of in-and-in breeding is to get a con- 

 siderable number of animals containing unmixed 

 the blood of some animal which shows excellent 

 characteristics desired by the breeder. Obviously 

 if outside blood were mingled with this blood other 

 tendencies would be introduced and the desired 

 characteristics would perhaps be lost. 



Cross breeding consists simply in crossing one 

 pure breed with another so that the offspring are 

 half breeds. This method has been resorted to 

 at frequent intervals, particularly in the breeding 

 of sheep. Similarly Thoroughbreds have been 

 crossed with various other breeds of horses as 

 indicated in the above discussion. As a rule 

 however, this method is not to to be recommended 

 for the reason that when various tendencies are 

 mixed the results cannot be predicted with cer- 

 tainty and sometimes the undesirable points of 

 both parents are perpetuated in the offspring. 



The system of breeding described by some 

 authors as line breeding may be defined as a mere 

 extension of in-and-in breeding after the latter 

 system has been in operation for several gener- 

 ations. In other words breeding takes place 



