362 ORGANIC EVOLUTION CONSIDERED 



of intermediate forms necessary to connect these 

 classes has not been discovered. 



Concerning reptiles, " The vertebrae are not intro- 

 duced into the definitions of the orders, since they 

 are not so exclusively distinctive as many other parts 

 of the skeleton." * Besides, it is not certain how 

 their various kinds of vertebras could have had a 

 common origin. 



Again, " The paleontology of the birds not being 

 known, our conclusions respecting the character of 

 their evolution must be incomplete." The derivation 

 of feathers from scales of reptiles needs to be ex- 

 plained. 



He claims that the monotremes, the lowest known 

 mammals, have lost their teeth and " their condition 

 is evidently one of degradation." How did they lose 

 the numerous well-developed teeth of their reptilian 

 progenitors? 



Again, "In the marsupial order we have a great 

 range of dental structure, which almost epitomizes 

 that of the monodelph orders. The dentition of the 

 carnivorous forms is creodont; that of the kangaroos 

 is perissodactyle, and that of the wombats is rodent. 

 Other forms repeat the Insectivora." How was it 

 possible for so many independent evolutions of teeth 

 to have taken place in which similar teeth were pro- 

 duced in marsupials and true mammals. The fact 

 that they were independently formed is the strongest 

 possible argument against the theory that they were 

 evolved. The author, in another place, tries to solve 

 this difficulty, and many others, on mechanical prin- 

 ciples. 



He admits that the phylogeny of Cetacea, Sirenia, 

 Edentata and Marsupials has not yet been cleared up, 

 * Page 121. 



