The reason why the offspring of protoplasm progressed, and the offspring
of nothing else does so, is that the viscid nature of protoplasm allows
vibrations to last a very long time, and so very old vibrations get
carried into any fragment that is broken off; whereas in the case of air
and water, vibrations get soon effaced and only very recent vibrations
get carried into the young air and the young water which are, therefore,
born fully grown; they cannot grow any more nor can they decay till they
are killed outright by something decomposing them. If protoplasm was
more viscid it would not vibrate easily enough; if less, it would run
away into the surrounding water.