292 DARWINISM AND THE PROBLEMS OF LIFE 



homogeneous cluster of cells ; and from this is 

 developed the polyp stage, consisting of two layers of 

 cells. The development then continues its course. 



Geology can tell us nothing about the first living 

 things. Apart from the fact that they must have 

 appeared at a time of which no evidence has been 

 handed down to us, they may have had no hard parts, 

 and so could not possibly be fossilised. 



But may not these lowest animals have survived to 

 our own time, without having abandoned their unicellular 

 character ? As a matter of fact, there are not only 

 polyps to - day, but there are millions of minute 

 organisms in every drop of water that consist of a 

 single cell. These are the protozoa. 



Since the whole body of the protozoa is a single cell, 

 it cannot be large, nor have different organs, as the 

 organs consist of several cells of different kinds. It is 

 all the more wonderful to find that natural selection has 

 created an infinite variety of forms among the protozoa. 

 There are the amoebae, small pieces of protoplasm with 

 a nucleus, which move about something like beer-froth 

 on a glass plate. If a tiny alga-granule lies in the way 

 of one of these animals, it moves towards it and surrounds 

 it, and the alga finds itself inside the amoeba. Gradually 

 we see a change in the alga-granule. Its digestible 

 parts are assimilated by the protoplasm of the amoeba, 

 and the indigestible remainder is thrust out at some 

 point. 



The movement of the amoebae is merely a sort of 

 flow, with constant changes of its shape, but the 

 "flagellates" have on their cell-body one or two lashes 



