94 DOCTRINE OF EVOLUTION 



Following the fishes, the amphibia arose during the 

 coal age or Carboniferous, usurping the proud position 

 of the lower vertebrate class. The reptiles then ap- 

 peared and gained ascendancy over the amphibia, to 

 become in the Mesozoic age the highest and most varied 

 of the existing vertebrates. At that time there were 

 the great land dinosaurs with a length of 80 feet, like 

 Brontosaurus ; aquatic forms like Ichthyosaurus and 

 Plesiosaurus, whose mode of evolution from terrestrial 

 to swimming habits was hke that of seals and penguins 

 of far later eras. Flying reptiles also evolved, to set an 

 example for the bats of the mammalian class, for both 

 kinds of flying organisms converted their anterior 

 limbs into wings, although in different ways. 



During the Triassic and Jurassic periods of the Meso- 

 zoic age, the first birds and mammals appeared to follow 

 out their diverging and independent lines of descent. 

 Palaeontology makes it possible to trace the origin and 

 development of many of the different branches that 

 grew out of the mammalian limb from different places 

 and at different times during the Mesozoic and the 

 following age, called the Cenozoic, or age of recent ani- 

 mals. It is unnecessary, however, for us to review more 

 of the details : the main result is obvious ; namely, 

 that the appearance of the great classes of vertebrates 

 is in the order of comparative anatomy and embryology. 

 Not only, then, is the fact of evolution rendered trebly 

 sure, but the general order of events is thrice and in- 

 dependently demonstrated to be one and the same. 

 Surely we must see that no reasonable explanation 

 other than evolution can be given for these basic facts 

 and principles 



