10 



RKLICS Ob' I'KIMKVAL LIFE 



troduction of life in our planet, and in what form 

 or forms it api3carcd. Wc may, therefore, neglect 

 all the vertebrate animals and the air-breathing 

 invertebrates, and may restrict our inquiries to 

 marine invertebrates. 



In relation to these, six of the larger divisions 

 or provinces of the Animal Kingdom may suffice 

 to include all the lower inhabitants of the ocean, 

 whether now or in some of the oldest fossil iferous 

 rocks. * 



Looking more in detail at our diagram, we 

 observe that the higher vertebrates nearest to man 

 in structure extend back but a little way, or, with 

 a few minor exceptions, only as far as the begin- 

 ning of the Kainozoic or Tertiary i'criod, in the later 

 part of which we still exist. Other air-breathing 

 vertebrates, the birds and the true rei^tiles, extend 

 considerably farther, to the beginning of the previous 

 or Mesozoic Period. The amphibians, or frog-like 



' Some modern zoologists, having perhaps, like some of the 

 old Greeks, lost the idea of the unity of nature, or at least that 

 of one presiding divinity, j)refer for the larger divisions of 

 animals the term phylum or p/iylon, implying merely a stock, 

 race or kind, without reference to a definite place in an ordered 

 kosmos. 



