And so on, almost _ad infinitum_.
Observe the dog, the birds of different species, the monkeys, the hares, and you find wonderful differences of habit, each adapting the animal differently, but with equal effectiveness, to the life which he in particular is called upon to lead.

The ants and bees are notoriously expert in the matter of instinct.

They have colonies in which some of the latest principles of social organization seem to find analogues: slavery, sexual regulations, division of labour, centralization of resources, government distribution of food, capital punishment, etc.
All this--not to stop upon details which the books on animal life give in great abundance--has furnished grounds for speculation for centuries, and it is only in the last generation that the outlines of a theory of instinct have been filled in with substantial knowledge.

A rapid sketch of this theory may be drawn in the following pages.
1.

In instinct in general there is a basis of inherited nervous tendency toward the performance of just the sort of action which the instinct exhibits.