64 THE PEJEVALSKY HOESE. 



one in regarding it as a feature possessed by the common ancestor 

 of the ass and the horse. 



Parallel with fairly material points of similarity, exist essential 

 differences between the Prjevalsky horse and the Tarpan ; such 

 are, the presence of a fore-lock in the Tarpan, the longer mane 

 (vide the Commission which examined the Crimean Tarpan) in 

 ihis animal, and the presence of a tail which in some waya 

 resembles that of the domestic horse. All these characters indi- 

 cate that the Tarjoan is a form more specialised in the direction 

 of the horse than is S. prjevalskii. The examination of the 

 Crimean specimen certainly showed that the most essential feature 

 of distinction between the horse and the ass — ^the callosities of the 

 posterior limbs — is wanting in the Tarpan. On this point, how- 

 ever, one cannot regard finality as having been reached ; firstly, 

 because only one specimen of the Tarpan has been investigated ; 

 and, secondly, because in certain races of the horse the callosities 

 are absent and yet there are all the other characters of the horse 

 and none of the ass. 



The Prjevalsky horse represents a generalised form intermediate 

 between the horse and the ass ; and this leads to the assumption 

 that it is more closely allied to the common stem-form of the horse 

 and the Asiatic ass than is any other species of Equus. Herein 

 rests the great importance of E. 2Jrjevahl'ii. In what genetic 

 relationship does it stand to the domestic horse? Has it given 

 origin to any of the ancestors of the domestic horse? Had it, in 

 the past, a wider geographical distribution than it has to-day? 

 These questions cannot be answered definitely, for, at the present 

 time, we have only very little actual foundation upon which to 

 base the answers. 



ADDENDUM. 



When my paper was already in the press, two communications 

 by Professor Noack (Equus Przevalskii and Die Entwickelung 

 des tSchadels von Equus Przevalskii) appeared in the ZooJogis- 

 cher Anzeiger (Nos. 663 and 664). Both articles are founded upon 

 the study partly of living material and partly of material in the 

 form of skins and skeletons obtained from Herr Hagenbeck of 

 Hamburg. I am very glad that Noack also has observed the 

 shoulder stripe, which I reported at the Natural History Congress 

 held in St. Petersburg (see " Report of this Congress," p. 194), and 



