CROSS-BREEDING 251 



duced by crossing the domestic mare to the jack. In 1915 

 there were 4,479,000 mules in the United States. This 

 was more than one-fifth of the total number of horses 

 in the country at the same time. The production of 

 mules has increased at a more rapid rate than horses, and 

 the use of mules is becoming more extensive. The mule 

 hybrid is a remarkable example of the practical advantages 

 which follow a particular cross. This animal is more 

 hardy and enduring than either parent. As compared 

 with the horse, the mule is longer-lived, less subject to 

 disease or injury, and more efficient in the use of food. 

 The mule can be safety put to work at a younger age, will 

 thrive on coarser feed, and seems to be much better able 

 to avoid many dangers which menace the usefulness of 

 the horse. The mule will perform more arduous labor 

 on less food. The mule will endure the heat of southern 

 latitudes more successfully than the horse and is there- 

 fore a popular draft animal in the South. 



The cross between the mare and jack is readily accom- 

 plished and the union is perfectly fertile. The conforma- 

 tion of the mule more closely resembles that of his sire. 

 The ears are long, feet long and narrow, withers sharp, 

 mane and tail scanty, and the voice a bray like the jack. 

 The mule is sterile. A few cases of supposed fertility of 

 mare mules have been reported, but the writer has investi- 

 gated several apparently reliable reports and has never 

 found an authentic case of a fertile mule. Most of the 

 erroneous reports of fertile mules have apparently arisen 

 from the not infrequent cases of mare mules which have 

 been observed suckling mule foals. The milk glands of 

 mare mules have been known to function as the result 

 of the stimulation afforded by a suckling foal. A case 

 of a mare mule giving milk was reported to the writer 



