SPONTANEOUS GENEEATION 219 



It seems likely that of all the organisms known to us these 

 Bacteria come nearest to the first living things, and yet they 

 probably stand very far from them and represent a much later 

 stage in the process of evolution. Minute and apparently 

 simple as the Bacteria are, it seems more than probable that the 

 first living things were very much smaller and simpler, so that 

 even if we had them under the highest powers of our micro- 

 scopes we should be unable to recognize them. Weismann has 

 suggested that they may have been single biophors, i.e. vital 

 units of the first order, such as he believes to constitute the 

 ultimate living particles of protoplasm, and he has actually 

 proposed the name " Biophoridae " for these hypothetical free- 

 living primordial organisms. 



These considerations throw a new light upon the question 

 of spontaneous generation, for if living matter is first formed 

 in such ultra-microscopic particles and can only be recog- 

 nized as living matter after it has reached a comparatively 

 high stage of evolution, it is obvious that we are not entitled to 

 say that it is never formed from not-living matter at the present 

 day. We cannot see it being formed, and we probably never 

 shall see it being formed, but it is possible that it is still 

 being "spontaneously generated" all the same. We are not 

 logically obliged, as we said before, to content ourselves with a 

 single starting point for organic evolution, and it would be quite 

 impossible to prove that all the different kinds of Bacteria, the 

 simplest organisms known to us, have descended from a single 

 ancestor. They may equally well have been derived from a 

 number of ancestral protoplasmic units which originated inde- 

 pendently from inorganic, not-living matter. If such an event 

 can have taken place once it may have taken place many times, 

 and may still be taking place around us, though the imperfect 

 means of observation at our disposal will not allow us to demon- 

 strate the fact. We may safely affirm, however, that no living 

 organism which we are at present capable of recognizing as such 

 has arisen, or ever will arise, by spontaneous generation, but that 

 all organisms known to us have been derived from pre-existing 

 organisms by some process of reproduction ; that, in the course 

 of long ages, they have undergone slow changes, whereby they 

 have become more and more diversified and usually more com- 

 plex in structure, and that in this way the evolution of the 

 animal and vegetable kingdoms has been brought about. 



