THE EVOLUTION OF MAN. 



CHAPTER XV. 



THE DURATION OF HUMAN TRIBAL HISTORY. 



Comparison of Ontogenetic and Phylogenetic Periods of Time. — Duration of 

 Germ-history in Man and in Different Animals. — Extreme Brevity of 

 the Latter in Comparison with the Immeasurable Long Periods of 

 Tribal History. — Relation of this Eapid Ontogenetic Modification to the 

 Slow Phylogenetic Metamorphosis. — Estimate of the Past Duration of 

 the Organic World, founded on the Relative Thickness of Sedimentary 

 Rock-strata, or Neptunian Formations. — The Five Main Divisions in 

 the Latter : I. Primordial, or Archilithic Epoch. II. Primary, or 

 Palaeolithic Epoch. III. Secondary, or Mesolithic Epoch. IV. Tertiary, 

 or Csenolithic Epoch. V. Quaternary, or Anthropolithic Epoch. — The 

 Relative Duration of the Five Epochs. — The Results of Comparative 

 Philology as Explaining the Phylogeny of Species. — The Inter-relations 

 of the Main Stems and Branches of the Indo-Germanic Languages are 

 Analogous to the Inter-relatious of the Main Stems and Branches of 

 the Vertebrate Tribe. — The Parent Forms in both Cases are Extinct. — 

 The Most Important Stages among the Human Ancestral Forms. — 

 Monera originated by Spontaneous Generation. — Necessity of Sponta- 

 neous Generation. 



"In vain as yet has it been attempted to draw an exact line of demarcation 

 between historic and prehistoric times ; the origin of man and the period of 

 his first appearance pass back into indefinable time ; the so-called archaic 

 age cannot be sharply distinguished from the present age. This is the fate 

 of all geological, as of all historical periods. The periods which we dis- 

 tinguish are, therefore, more or less arbitrarily defined, and, like the divisions 



