262 THE DOCTRINE OF DESCENT. 



ferentiation of structure is to be observed, as in the 

 Lacertilia, or Crocodilia, it goes no further than a modi- 

 fication of the form of the articular surfaces of the verte- 

 brae, or of the degree to which the internal nasal aper- 

 tures are surrounded by bone. The osteological differ- 

 ences, which alone are exhibited by fossil remains, have 

 doubtless been accompanied by many changes in the 

 organization of the destructible parts of the body; but 

 everything tends to show that the amount of change in 

 the organization of reptiles since their first known ap- 

 pearance upon the earth, is not great in itself; and is 

 wholly insignificant, if we take into consideration the 

 lapse of time, and the changes of the surface of the 

 globe, which are represented by the Mesozoic and Ter- 

 tiary formations. 



" From the point of view of the evolution hypothesis, 

 it is necessary to suppose that the Reptilia have all sprung 

 from a common stock, and I see no justification for the 

 supposition that the rapidity of their divergence from 

 this stock was greater before the epoch of the Trias than 

 it has been since. Consequently, seeing that the approx- 

 imation of the oldest known representatives of the differ- 

 ent orders is so slight, reptiles must have lived before 

 the Trias for a length of time, compared with which that 

 which has elapsed from the Triassic epoch until now is 

 small — in other words, the commencement of the ex- 

 istence of reptiles must be sought in a remote palaeozoic 

 epoch." 



Comparison thus points us back to ages which aflord 

 no record of the actual derivation of this class. Even 

 the Ichthyosauria and Plesiosauria, so frequently men- 

 tioned in conjunction, deviate widely from one another 



