This means that its constituent elements form a system.
They stand to each other in relations of mutual support.

In short, life is possible because there is balance.
This general state of balance, however, is able to go along with a lot of special balancings that seem largely independent of each other.
It is important to remember this when we come a little later on to consider the instincts.

All sorts of lesser systems prevail within the larger system represented by the individual organism.

It is just as if within the state with its central government there were a number of county councils, municipal corporations, and so on, each of them enjoying a certain measure of self-government on its own account.

Thus we can see in a very general way how it is that so much variation is possible.