298 GEOLOGICAL CONTEMPORANEITY ix 



less differentiated, than Beryx lineatus of King 

 George's Sound ? 



Or to turn to the higher Vertebrata in what 

 sense are the Liassic Chelonia inferior to those 

 which now exist? How are the Cretaceous 

 Ichthyosauria, Plesiosauria, or Pterosauria less 

 embryonic, or more differentiated, species than 

 those of the Lias? 



Or lastly, in what circumstance is the Phasco- 

 lotherium more embryonic, or of a more genera- 

 lised type, than the modern Opossum; or a 

 Lophiodon, or a Palceotherium, than a modern 

 Tapirus or Hyrax? 



These examples might be almost indefinitely 

 multiplied, but surely they are sufficient to prove 

 that the only safe and unquestionable testimony 

 we can procure positive evidence fails to dem- 

 onstrate" any sort of progressive modification 

 towards a less embryonic, or less generalised, type 

 in a great many groups of animals of long- 

 continued geological existence. In these groups 

 there is abundant evidence of variation none of 

 what is ordinarily understood as progression ; and, 

 if the known geological record is to be regarded 

 as even any considerable fragment of the whole, 

 it is inconceivable that any theory of a necessarily 

 progressive development can stand, for the numer- 

 ous orders and families cited afford no trace of 

 such a process. 



But it is a most remarkable fact, that, while the 



