It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change, that lives within the means available and works co-operatively against common threats.

... probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.

Daily it is forced home on the mind of the biologist that nothing, not even the wind that blows, is so unstable as the level of the crust of this earth.

And hail their queen, fair regent of the night.

If man had not been his own classifier, he would never have thought of founding a separate order for his own reception.

Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relationship to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring.

It may be doubted that there are many other animals which have played so important a part in the history of the world as have these lowly organized creatures.