1895.] NATURAL SCIENCES OF PHILADELPHIA. 263 



Not many years after the horse had been introduced into South 

 America by the Spaniards, the crew of a vessel, sailing along the 

 coast, saw a number of horses at a point several hundred miles 

 distant from the small settlements to which horses bad been 

 brought from Europe. It is considered questionable that horses 

 which may have escaped from these settlements could have increased 

 in a few years sufficiently to extend several hundred miles away. 

 That the horses thus seen were native animals is possible, though 

 very doubtful, since it seems probable that the native American 

 horse, though of the same species with the European, may have 

 presented some varietal differences in appearance. All that we 

 can say is that this incident leaves the question of the extinction 

 of the South American horse open to some, though a very slight, 

 degree of doubt. If, as is probable, it became extinct, the cause of 

 its extinction must remain an unsolved mystery. In short, the 

 whole subject of animal extinction is one that is rife with difficulties. 

 The best that can be done is to offer some suggestion of causes that 

 may have aided in the disappearance of species: It is quite probable, 

 however, that many influences were at work of which we are ignor- 

 ant, and most of which will always remain beyond the scope of 

 human investigation or conjecture. 



