The selective organization, which from amongst the germinal elements precipitates ever so many and different forms of fresh life, is so loose and elastic that a working arrangement between the parts can be reached in all sorts of directions.

The lesser systems are so far self-governing that they can be trusted to get along in almost any combination; though of course some combinations are naturally stronger and more stable than the rest, and hence tend to outlast them, or, as the phrase goes, to be preserved by natural selection.
It is time to take account of the principle of natural selection.

We have done with the subject of variation.

Whether use and disuse have helped to shape the fresh forms of life, or whether these are purely spontaneous combinations that have come into being on what we are pleased to call their own account, at any rate let us take them as given.

What happens now?
At this point begins the work of natural selection.