128 SPONTANEOUS GENERATION. 



ages of extremely simple organisms. To the general 

 cohesion of the theory, therefore, it is unimportant 

 whether we affiliate each of these living motes to a 

 parent like itself, or to a combination of chemical sub- 

 stances previously without life. 



Considering the vast results attributed to the prin- 

 ciple of variability) it has been thought strange that 

 any organisms should through great cycles of time have 

 escaped its operation, and transmitted their original 

 simplicity to an endless succession of descendants. 



On the hypothesis of spontaneous generation working 

 continuously this difficulty would disappear ; simple 

 organisms would be continually losing their simplicity 

 by variation, but new organisms of equal simplicity 

 would continually appear in the world, spontaneously 

 generated. 



It might still be true that all but the least conspicuous 

 members of the world's population belong to a single 

 family, or to an extremely small number of separate 

 lines of descent. If we suppose that, as soon as the 

 globe was fitted for living occupants, a single simple 

 organism was spontaneously generated, or, if you please, 

 created, or, in any other way that may be named, intro- 

 duced upon the earth, the results in accordance with 

 actual facts may be logically deduced agreeably to the 

 various principles of the theory of development. Its 

 descendants would multiply and replenish the earth, 

 unchecked, in all parts suited to their conditions of 

 existence, till all such parts were occupied. No further 

 advance in the population of the world could then take 



