212 FOUNDATIONS OF BIOLOGY 



foundations. To say, therefore, in the admitted absence of 

 evidence, that I have any belief as to the mode in which exist- 

 ing forms of life have originated, would be using words in a 

 wrong sense. But expectation is permissible where belief is 

 not; and if it were given to me to look beyond the abyss of 

 geologically recorded time to the still more remote period 

 when the Earth was passing through physical and chemical 

 conditions, which it can no more see again than a man can 

 recall his infancy, I should expect to be a witness of the 

 evolution of living protoplasm from not living matter. . . . 

 That is the expectation to which analogical reasoning leads 

 me; but I beg you once more to recollect that I have no right 

 to call my opinion anything but an act of philosophical faith." 

 Since so far as is known all life now arises from preexisting 

 life and has done so since matter first assumed the living state, 

 it apparently follows that the stream of life is continuous 

 from the remote geological past to the present and that all 

 organisms of to-day have an ancient pedigree. It is to the 

 establishment of this as the reasonable conclusion from the 

 data accumulated during recent years, that from now on our 

 attention is somewhat more particularly directed; and ac- 

 cordingly it is necessary first of all to consider in some detail 

 the genetic connection of present-day forms as exhibited in 

 reproduction. 



B. REPRODUCTION 



The power of producing new individuals specifically similar 

 to the parent is, as has been seen, one of the most important 

 characteristics of living in contrast with lifeless matter, and 

 is exhibited in its simplest form in the unicellular plants and 

 animals. In Paramecium the nucleus and cytoplasm divide 

 into two parts, so that by cell division, here called BINARY 

 FISSION, the identity of the parent organism is merged into 



