PHYLETIC BRANCHES AMONG THE VERTEBRATES 169 



donts, and of the Primates, have an evolution not 

 confined to the Eocene epoch, and must in some as 

 yet unknown country cast deep roots into Secondary 

 times. In any case, a jump such as those described, 

 which would transform in the period elapsed since 

 the Oligocene a Palseotherium into a Horse, and in 

 that since the middle Miocene an Amphicyon into a 

 Bear, does not correspond to the real facts. 



As we have seen above, in the case of the In- 

 vertebrates, the phyletic branches are, in a general 

 way, extremely long, and continue parallel without 

 meeting during a long geological period. With 

 these reservations, I will endeavour to show that 

 all the laws of evolution of the phyletic series, 

 established by the help of the lower animals, are 

 met with among the Vertebrates without any ex- 

 ception whatever. 



It is only, we may say, in the last few years that 

 palaeontologists have set themselves in a connected 

 fashion to precisely reconstruct the phyletic branches 

 among the Vertebrates, and more especially among 

 the Mammals. Yet it has been long known that 

 a few types of the lower Vertebrates manifest 

 great geological longevity. The Squalaceous [shark- 

 like] type seems to have varied little since its first 

 appearance at the end of the Silurian. Thus the 

 grey Sharks of the genus Notidanus have left certain 

 remains in the Lias, and had perhaps precursors 

 in the Coal. 



The Sharks of the Cestracion type, which inhabit 

 the warm regions of the Pacific, have, as ancestors, 

 the Acrodus of the Secondary and the Orodus of the 

 Carboniferous era, and the branch probably goes 



