THE NATIONAL ZOO AT WASHINGTON. 707 



illustrate: An antelope passes along a certain plain, eats at one place, 

 drinks at another, lies down at a third, is pursued ])y a wolf for half a 

 mile, when the wolf gives up the unequal race, and the antelope escapes 

 at his ease. A second antelope comes along. The foot scent from the 

 interdigital glands marks the course of his relative as clearly for him 

 as the track in the snow would for us. Its strength tells him some- 

 what of the time elapsed since it was made, and its individuality tells 

 him whether his predecessor was a stranger or a personal friend, just 

 as surely as a dog can tell his master's track. The frequency' of the 

 tracks shows that the first one was not in haste, and the hock scent, 

 exuded on the plants or ground when he lay down, informs the second 

 one of the action. At the place where the wolf was sighted, the sudden 

 diii'usion of the rump musk on the surrounding sagebrush will be per- 

 ceptible to the newcomer for hours afterwards. The wide gaps between 

 the traces of foot scent now attest the speed of the fugitive, and the 

 cause of it is clearly read when the wolf trail joins on. This ma}' sound 

 a far-fetched tale of Sherlock Holmes among the animals, but not so 

 if we remember that the scent faculty is better than the sight faculty 

 in these animals, while their sight faculty is at least as good as ours, 

 and that, finally, if all this had been in the snow we also could have 

 read it with absolute precision. 



The pronghorned antelope, or prongbuck of books, is the only 

 horned ruminant in North America that has onh^ two hoofs on each 

 foot. Nature's economic plan has been to remove all parts that cease 

 to be of use, and so save the expense of growing and maintaining them. 

 Thus man is losing his back or wisdom teeth since civilized diet is 

 rendering them useless. The ancestor of the antelope had four hoofs 

 on each foot, like a deer or a pig, but the back pair on each foot has 

 been dropped. At an earlier step the common ancestor of antelope 

 and deer had five well-developed toes on each extremity, but it seems 

 that while this makes an admirable foot for wadding in treacherous 

 swamps, it is for mechanical reasons a slow foot; the fewer the toes 

 the greater the speed. The deer still living in swamps could not 

 afford to dispense entirely with the useful little hind or mud hoof. 

 There they are still for bog use, though much modified from the original 

 equal-toed type, more nearly shown in the pig. But the antelope, 

 living on the hard, dry uplands had no use for bogtrotters, and 

 exchanged them for a higher rate of speed, so that it now has only two 

 toes on each foot. 



The horse family went yet further, for they lived in a region where 

 evolution went faster. The}' shunned the very neighborhood of swamps ; 

 all their life was spent on the firm, dry, level country; speed and sound 

 feet were their very holds on life, and these they maintained at their 

 highest pitch by adopting a foot with a single hoof -clad toe. 



There is one other remarkable peculiarity of the antelope to note, 



