THE WONDER OF LIFE 575 



It is a grand piece of history beyond doubt — ^the pre- 

 historic history of the organic world. If our conception 

 is right at aU, there once was a time when the living creatures 

 of the Earth were very minute corpuscles of living matter 

 — ^very simple but individuated, able to feed, grow, and 

 multiply, able to enregister their experiences. We must 

 try to think of them as simpler than any of the Protists 

 that are visible to-day. Perhaps the ultra- microscopic 

 Chlamydozoa may be nearest to them. 



Great Steps in Evolution. — ^Looking backwards we 

 see a great succession of achievements. Within the realm 

 of the uniceUulars we find every grade of structural differen- 

 tiation — some relatively simple, some extraordinarily 

 complex like many of the Radiolarians. We can still 

 trace the gradual specialization of functions, the estabhsh- 

 ment of the great types of ceU hfe, the beginnings of repro- 

 duction and of death. One of the earhest steps was the 

 dichotomy which separated plants and animals — ^the most 

 momentous cleavage in evolution. 



A simple instance may serve to bring out the point that 

 functions have become more speciaUzed as evolution pro- 

 ceeded. W. Staniewiez has called attention to the interest- 

 ing fact that Protozoa have never learned to digest fat. 

 AU multicellular animals have this power, but the Protozoa 

 have not. Experiments with Paramceciima, Stentor, 

 and some other common Infusorians show that fat may 

 be ingested, but it is not digested. It is not a natural 

 part of a Protozoon's food, and the fat that is occasionally 

 found ia natural conditions within the Protozoon cell 

 seems to be due to the transformation of proteids or carbo- 

 hydrates. If the facts are correct, the power of digesting 

 fat was added on to the digestive function when the transi- 



