The most violent appetites in all creatures are _lust_ and _hunger_; the first is a perpetual call upon them to propagate their kind; the latter to preserve themselves.
3. It is astonishing to consider the different degrees of care that descend from the parent to the young, so far as is absolutely necessary for the leaving a posterity. Some creatures cast their eggs as chance directs them, and think of them no further, as insects, and several kinds of fish; others, of a nicer frame, find out proper beds to deposit them in, and there leave them, as the serpent, the crocodile, and ostrich; others hatch their eggs and tend the birth till it is able to shift for itself.
4. What can we call the principle which directs every different kind of bird to observe a particular plan in the structure of the nest, and directs all of the same species to work after the same model! It cannot be _imitation_; for though you hatch a crow under a hen, and never let it see any of the works of its own kind, the nest it makes shall be the same to the laying of a stick, with all the other nests of the same species. It cannot be _reason_; for were animals endued with it to as great a degree as man, their buildings would be as different as ours, according to the different conveniences that they would propose to themselves.
5. Is it not remarkable, that the same temper of weather, which raises this general warmth in animals, should cover the trees with leaves, and the fields with grass, for their security and concealment, and produce such infinite swarms of insects for the support and sustenance of their respective broods?
Is it not wonderful that the love of the parent should be so violent while it lasts, and that it should last no longer than is necessary for the preservation of the young?
6. With what caution does the hen provide herself a nest in places unfrequented, and free from noise and disturbances? When she has laid her eggs in such a manner that she can cover them, what care does she take in turning them frequently, that all parts may partake of the vital warmth? When she leaves them, to provide for her necessary sustenance, how punctually does she return before they have time to cool, and become incapable of producing an animal? In the summer, you see her giving herself greater freedoms, and quitting her care for above two hours together; but, in winter, when the rigour of the season would chill the principles of life, and destroy the young one, she grows more assiduous in her attendance, and stays away but half the time.