86 THE EIDDLE OF THE UNIVERSE. 



indubitably to a corresponding unicellular ancestor, a 

 primitive, Lauren tian protozoon. 



For the purpose of our monistic philosophy, how- 

 ever, it is a matter of comparative indifference how 

 the succession of our animal predecessors may be 

 confirmed in detail. Sufficient for us, as an incon- 

 testable historical fact, is the important thesis that 

 man descends immediately from the ape, and 

 secondarily from a long series of lower vertebrates. 

 I have laid stress on the logical proof of this " pithe- 

 cometra- thesis " in the seventh book of the General 

 Morphology : " The thesis that man has been evolved 

 from lower vertebrates, and immediately from the 

 simice, is a special inference which results with 

 absolute necessity from the general inductive law of 

 the theory of descent." 



For the definitive proof and establishment of this 

 fundamental pithecometra-thesis the palaaontological 

 discoveries of the last thirty years are of the greatest 

 importance ; in particular, the astonishing discoveries 

 of a number of extinct mammals of the Tertiary 

 period have enabled us to draw up clearly in its main 

 outlines the evolutionary history of this most impor- 

 tant class of animals, from the lowest oviparous 

 monotremes up to man. The four chief groups of 

 the placenta Is, the heterogeneous legions of the 

 carnassia, the rodentia, the ungulata, and the 

 primates, seem to be separated by profound gulfs, 

 when we confine our attention to their representatives 

 of to-clay. But these gulfs are completely bridged, 

 and the sharp distinctions of the four legions are 

 entirely lost, when we compare their extinct prede- 

 cessors of the Tertiary period, and when we go back 

 into the Eocene twilight of history in the oldest part 



