ORGANIC EVOLUTION — PHYSICAL 15 



and differently couditioned as to the environment, 

 would develop on divergent lines of evolution. 



The conclusion, deductively arrived at, that the con- 

 ditions under which life has existed and still exists, are 

 such that evolution must have occurred and still occurs, 

 is therefore decisively confirmed by the conclusion, 

 inductively arrived at, that evolution certainly has 

 occurred, and therefore, though in the subsequent pages 

 of this work many proofs will incidentally be afforded 

 of the actuality of Organic Evolution, in future it will 

 be assumed that the truth of it is admitted, and we 

 shall endeavour only to fill in the details of the map as 

 to the fidelity of the outlines of which no well-informed 

 man any longer entertains a doubt. 



The ujDward march of life from the earliest begin- 

 nings may be compared to that of a horde of men, 

 leaving their old habitations and entering new lands ; 

 travelling ever forwards, but ever sending out branch 

 swarms that part from the parent horde, never to 

 reunite with it, and ever leaving some of their members 

 behind on the way, some of whom may journey back- 

 wards; such hordes as those which in ancient times 

 came from the East, settled the countries they passed 

 over, sent offshoots to the North and South, and rolled 

 on the tide of conc^uest till they destroyed the old 

 Roman Empire. The lowest, or in other words the 

 least differentiated and specialized forms of life, may be 

 compared to those members of the horde that stayed 

 behind in the original habitat, the intermediate 

 forms to those that halted and settled by the way, and 

 the highest forms to those that journeyed till they 

 reached the farthest limits of the wanderings. The 

 comparison is made yet closer if we imagine, as generally 

 true of life, that which is generally true of emigrant 

 swarms of men, namely, that those that stayed in the 

 original habitat, that those that halted, diverged, or 



