ORIGIN OF SPECIES 207 



culty to the current theory of descent. Fixity of 

 type of certain species, geological evidence shows, 

 has persisted through millions of years. 

 Henry Fairfield Osborn writes: 



"Of the eighteen great orders of reptiles which 

 evolved on land, in the sea, and in the air, during 

 the long Reptilian Era of 12,000,000 years only 

 five orders survive today; namely, the turtles 

 (Testudijiata), tuateras {Rhynchocophalia) , lizard 

 {Lacertilia), and crocodiles {Crocodilia). 



"The evolution of the members of these five 

 surviving orders has either been extremely slow 

 or entirely arrested during the 3,000,000 years 

 which are generally assigned to Tertiary time; 

 we can distinguish only by relatively minor 

 changes the turtles and crocodiles of the base of 

 the Tertiary from those living today. In other 

 words, during this period of 3,000,000 years the 

 entire plant world, the invertebrate world, the 

 fish, the amphibian, and the reptilian worlds 

 have all remained as relatively balanced, static, 

 unchanged or persistent types."^^ 

 According to Jacques Loeb "the constancy of 

 species, i.e., the permanence of specificity may there- 

 fore be considered as established as far back as two 

 or possibly two hundred millions of years. The 



" The Origin and Evolution of Life, 231. 



