158 ANIMAL LIFE PAST AND PKESENT. 



tions of Northern Africa and Southern and Central 

 Asia are fully explored, we shall be rewarded by the 

 discovery of other kinds, which will tend to more or 

 less completely blend together those at present known 

 to us, and which will also show how these have gradu- 

 ally migrated, since the Eocene Period, from the great 

 continental northern mass to those southerly areas 

 wherein some have existed up to a comparatively late 

 period, and where others still remain as the sole living 

 witnesses in the Old World of a group which has all 

 but passed away. 



