10 THE EVOLUTION OF MAN. 



have been many millions of years. During that time there 

 came into existence by spontaneous generation the oldest 

 and simplest organisms — those in which life began upon oui 

 planet — viz., the Monera. From these, one-celled plants and 

 animals first developed — the Amoebae and many kinds of 

 Protista. During this same Archilithic Epoch, also, all the 

 invertebrate ancestors of the human race developed from 

 these one-celled organisms. We draw this conclusion from 

 the fact that towards the close of the Silurian period 

 a few remains of fossil Fishes are already to be found, viz., 

 Selachians and Ganoids. These are, however, much more 

 highly organized and of later origin than the lowest 

 Vertebrates (the Amphioxus), or than the various skull-less 

 Vertebrates allied to Amphioxus, which must have lived 

 during this time. The latter must necessarily have been 

 preceded by all the invertebrate ancestors of man. Hence 

 we may characterize this entire epoch as the " age of man's 

 invertebrate ancestors;" or, with special reference to the 

 oldest representatives of the Vei'tebrate tribe, as the " age 

 of Skull-less Animals." During the whole Archilithic Epoch 

 the inhabitants of our planet consisted exclusively of 

 aquatic forms ; at least, no remains of terrestrial animals 

 or plants dating from this period have as yet been found. 

 A few remains of land-dwelling organisms which are some- 

 times referred to the Silurian Period, are Devonian. 



The Primordial Epoch was followed by the PalaeoHthic, 

 Palaeozoic, or Primary Epoch, which is also separable into 

 three sub-periods : the Devonian, the Carboniferous, and the 

 Permian. During the Devonian Period the Old Red Sand- 

 stone, or Devonian system was formed ; during the Car- 

 boniferous, those great beds of coal were deposited which 



