CHAPTER XVII 



PHYLETIC BRANCHES AMONG THE VERTEBRATES 



Branches of rapid and of slow evolution among the Fishes, Amphi- 

 bians, and Reptiles Phyletic branches among the Mammals 

 Marsupials and Multituberculata Anthracotherids Proboscidians 

 Conclusions. 



IN studying the laws which govern the evolution 

 of phyletic series we have, until now, taken all our 

 examples from the Invertebrates, for the historical 

 reason that these animals have furnished Waagen, 

 Neumayr, and other palaeontologists with their 

 materials for study and the first really demonstrative 

 facts. 



The evolution of the Vertebrates remained for a 

 long time a stranger to these methods ; or, at any 

 rate, the specialists engaged upon them preferred 

 to take other lines. Instead of setting themselves 

 to follow step by step going back stratum by 

 stratum through the series of sedimentary deposits 

 the slow and gradual mutation of a given branch, 

 these palaeontologists thought themselves very early 

 in possession of documents sufficient to enable them to 

 retrace the genealogical links, not only of genera and 

 of families, but often of the orders and even of the 

 classes of the animal kingdom. These syntheses pos- 

 sess a brilliant side well calculated to captivate super- 



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