PROGRESS, BIOLOGICAL AND OTHER 17 



We know that there was a time when the earth, 

 hot and fiery, could not have been the abode of life. 

 Of the first origins of life we know nothing and guess 

 little. What we can justifiably surmise is that the 

 protoplasm of the original organisms was not yet dif- 

 ferentiated into cytoplasm and nucleus, and that sex- 

 uality had not yet arisen. The bacteria, however 

 specialized in other ways, are still in this primitive 

 condition. 



Later, we can with great probability infer that the 

 independent units into which the stuff of life was sub- 

 divided reached a size which, though still minute, 

 was at least not beyond or even close to the limits of 

 microscopic vision; they were further provided with 

 a nucleus, and occasionally underwent sexual fusion. 

 In other words, they showed an organization which 

 we call cellular; they were free-living cells. Such 

 unicellular creatures must have been at one epoch 

 sole inhabitants of the earth, and diverged into the 

 most manifold types of structure and modes of life. 

 Such of them as led an animal as opposed to a plant 

 type of existence would be classified under the Pro- 

 tozoa or unicellular animals.^ 



The colonial habit gives advantages of increased 

 size and greater rapidity of motion, of which many 



« There is a certain school of biologists who object to de- 

 scribing Protozoa as cells. This to others appears pedantic. 

 But, whether or no they are right in the matter of terminology, 

 the fact which I am here emphasizing remains, viz., that Pro- 

 tozoa had to be aggregated before the Metazoa, or many-celled 

 animals, could arise. 



