LIVING MAMMALIA AND THEIE ANCESTORS. 85 



not call these mixed forms, but forms bearing the 

 impress of different circumstances. 



But when brought into this connection with 

 the primeval world, the systematic arrangement of 

 the' Mammalia made in accordance with their 

 present state must above all things appear alto- 

 gether unsatisfactory. The Mammals, as the most 

 highly developed animals, not only, of course, 

 stand farthest from the beginnings of animal life, 

 but they have also at all events the Vertebrates 

 diverged more from one another than any 

 other class. For even the Eeptiles, whose day is,, 

 in every respect, long since past, are behind them 

 in this. However adaptable their limbs were to 

 circumstances (their teeth were less so), their brain 

 remained stationary. It was only with the charac- 

 teristic advance in the organisation of the Mam- 

 malia that scope was given to a progressive brain. 

 The attempts which have repeatedly been made to 

 make use of this point also for a systematic arrange- 

 ment of the Mammalia, have either been too one- 

 sided, or could not show any satisfactory result, 

 owing to the large gaps in our palseontological 

 knowledge. It is reserved for the future to make 

 the systematic classification of the Mammalia a 

 really ' natural ' one, and one which shall attain the 



