PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 509 



these pests; thus the falling mane of the northern horse is distinctly dis- 

 advantageous as compared with the upright mane of the asses and zebras. 

 Ticks abound in the southern plains region of the United States, as well as 

 in the forests bordering the IMexican plateau, and are thus both plains and 

 forest pests. They are certainly to be considered in connection with the 

 extermination of horses. 



