40^ THE WORLD OF LIFE 



space, food, etc.) that the Paramecivim could go on increasing 

 for 350 generations, that is to say, for about two years, the 

 produce would he sufficient in bulk to occupy a sphere larger 

 than the known universe! 



I^ow taking this as a type of the Protozoa — the one-celled 

 animals and plants that still exist in thousands of varied forms 

 — we see in imagination the beginnings of the vast world of 

 life ; and we also see the absolute necessity — if it was to con- 

 tinue and develop as it has done, filling the earth with infinite 

 variety, and beauty, and the joy of life — for higher and 

 higher forms to come successively into being, and for these 

 forms to exist upon the food provided by the bodies of the 

 lower. It follows that almost simultaneously with the first 

 plant-cells which had the power of extracting carbon from the 

 carbonic acid gas in the air and water and converting it into 

 protoplasm, the first animal cells must also have arisen; and 

 both must very rapidly have diverged into varied forms in 

 order to avoid the whole of the water from being monopolised 

 by some one form of each, and thus checking, if not altogether 

 preventing, the development of higher and more varied forms. 

 Variation and selection were thus necessary from the very first 

 — ^ were even far more necessary than at any later period, in 

 order to avoid the possibility of the whole available space being 

 occupied by some very low form to the exclusion of all others. 

 Some writers have thought that, owing to the very uniform 

 conditions in the primeval ocean, the development of new forms 

 of life would then proceed more slowly than now. But a con- 

 sideration of the enormously rapid increase of primitive life 

 leads to the conclusion that the reverse was the case. It seems 

 more probable that evolution proceeded as much more rapidly 

 than now, as the rate of increase of the lower animals is more 

 rapid than that of the highest animals. This view is supported 

 by the fact, observed long ago in the Foraminifera, that their 

 variability was immensely greater than in any other animals ; 

 and this will serve to shorten the time required for the develop- 



