CHAPTEE Vr. 



THE EXTINCT MAMMALIA OF THE OLD WORLD. 



Although it may seem somewliat out of place to begin the 

 systematic treatment of our subject with extinct rather than 

 with living animals, it is necessary to do so in order that we 

 may see the meaning and trace the causes of the existing dis- 

 tribution of animal forms. It is true, that the animals found 

 fossil in a country are very generally allied to those wliich still 

 inhabit it ; but this is by no means universally the case. If it 

 were, the attempt to elucidate our subject by Palaeontology 

 would be hopeless, since the past would show us the same 

 puzzling diversities of faunas and floras that now exist. We 

 find however very numerous exceptions to this rule, and it is 

 these exceptions which tell us of the past migrations of whole 

 groups of animals. We are thus enabled to determine what 

 portion of the existing races of animals in a country are de- 

 scendants of its ancient fauna, and which are comparatively 

 modern immigrants ; and combining these movements of the 

 forms of life with known or probable changes in the distribution 

 of land and sea, we shall sometimes be able to trace approxi- 

 mately the long series of changes which have resulted in the 

 actual state of things. To gain this knowledge is our object in 

 studying the " Geographical Distribution of Animals," and our 

 plan of study must be determined, mainly, by the facilities it 

 affords us for attaining this object. In discussing the countless 

 details of distribution we shall meet with in our survey of the 

 zoological regions, we shall often find it useful to refer to the 

 evidence we possess of the range of the group in question in 



