ARCHEAN AND PALEOZOIC LIFE 425 
With this period ends the Paleozoic, within which 
is preserved and recorded the ancient history of life 
upon the earth. By the close of the Paleozoic, many 
of the groups of plants and animals that now people 
the earth, have already come into existence. It may 
be said that the most typical Paleozoic animals are 
the marine invertebrates, but vertebrates of ancient 
types have developed. Neither fishes, amphibia, nor 
reptiles have close resemblance to the species of the 
same groups at present in existence. The same also 
is true of the land plants. They are of ancient forms 
in distinction from those of the present, which we 
call modern. The next period, the Mesozoic, is the 
time of the Middle Ages of life history. The close 
of the Paleozoic is the natural dividing line between 
two different epochs of time. Invertebrates predomi- 
nate in the Paleozoic, but vertebrates take precedence 
in the next division. HKven among the invertebrates 
there are differences of vast importance upon the 
two sides of this dividing line. 
