252 THE BREEDING OF ANIMALS 



by L. O. Swarner of Boonville, Missouri, in 1913. This 

 mare was six years old and at the time had been giving 

 milk for five weeks. The milk glands had not been stimu- 

 lated in any way, but the milk " streamed " from the 

 udder. It is also of interest to know that this mare mule 

 showed unmistakable evidences of what in the ordinary 

 mare would be regarded as complete sexuality. She 

 came in heat regularly. The mule was bred frequently 

 when in season to both the stallion and jack, but failed 

 to conceive. A sample of the milk was analyzed by the 

 Chemical Department and found to contain 2.46 per cent 

 protein, 5.8 per cent sugar, 1.45 per cent fat, and .4 per 

 cent ash. (See Plate III.) 



The mare mules apparently have all the essential 

 organs of reproduction and come in heat with considerable 

 regularity. The horse mule also has the essential sexual 

 organs well developed and his sexual instincts are so well 

 developed that castration of young mules is universally 

 practiced. The cause of sterility in the horse mule is not 

 due to a failure to develop spermatozoa, but the sperm- 

 cells are imperfect. In some cases the sperm-cells lack 

 the tail or flagellum. 



237. The hinny hybrid. The reciprocal cross between 

 the jennet and the stallion is accomplished without 

 difficulty and the union is very fertile. The hybrid from 

 the cross is called a hinny. Some authorities have held 

 that the hinny resembled the horse much more closely 

 than the mule, but this is denied by most practical breeders. 

 The hinny is not commercially important as the jennet 

 is too valuable for the production of jacks to be used for 

 crossing. The hinny is sterile. (See Plate XVIII, upper.) 



238. Crossing the horse and the zebra. The horse 

 and zebra have been successfully crossed by Ewart of 



