ch. vni ] THE BEGINNINGS OF LIFE. 423 



In the next place the overthrow of the dogma of fixity 

 of species, and the consequent general displacement of the 

 Doctrine of Creation by the Doctrine of Evolution, have 

 made the scientific world familiar with the conception of the 

 development of the more specialized forms of life from less 

 specialized forms ; and thus the development of the least 

 specialized forms of life from the most complex forms of 

 not-life ceases to seem absurd, and even acquires a sort of pro- 

 bability. And finally, the researches of geologists, showing 

 that our earth's surface was once " melted with fervent heat," 

 and confirming the theory of the nebular origin of our planet, 

 have rendered it indisputable that there must once have been 

 a time when there was no life upon the earth ; so that cer- 

 tainly at some time or other, though doubtless not by a 

 single step but by a number of steps, the transition irom 

 not- life to life must have been made. Hence the doctrine 

 omne vivum ex vivo, as now held, means neither more nor less 

 than that every assemblage of organic phenomena must have 

 had as its immediate antecedent some other assemblage of 

 phenomena capable of giving rise to it : in other words, the 

 doctrine has become little more than a specialized corollary 

 from the persistence of force. In the case of all save the 

 lowest organisms, the only antecedent phenomenon capable oi 

 giving rise to the organism in question has been inductively 

 proved to be some other organism. But in the case of the 

 lowest organisms it is theoretically possible that the requisite 

 antecedent may in some instances be an assemblage of un- 

 organized materials ; and it remains for induction to show 

 whether this possibility is ever actually realized or not, 

 under existing terrestrial conditions. 



Such being the modification which modern discoveries 

 have imposed upon the doctrine omne vivum ex vivo, it need 

 hardly be added that the hypothesis of spontaneous genera- 

 tion has undergone a no less important change. The theory 

 that an organism which is to any extent specialized in struc- 



