PROTOZOA 323 



strongest biogens will age, and thus bring life to a 

 natural termination, we do not know. But we can 

 affirm with some confidence that one day a violent 

 death will make an end of all terrestrial life. The 

 cooling of our planet is proceeding with inexorable 

 necessity, and the day will come when the warm 

 earth of our time will course through space as a cold 

 and waterless sphere. All life will perish in this 

 state of icy rigidity. 



