This nervous tendency shows itself independently of learning by the individual in a great many cases, as in the instinct of sucking by young animals, pecking for food by young fowls, the migrating actions of adult mammals and birds, the courting movements of many varieties of animal species.

In all this we have what is called the "perfect" instinct.

To be perfect, an instinct must be carried out successfully by the animal when his organism is ready, without any instruction, any model to imitate, any experience to go upon.

The "perfect" instincts are entirely congenital or inborn; the nervous apparatus only needs to reach the proper stage of maturity or growth, and forthwith the instinctive action is performed as soon as the external conditions of life are such as to make its performance appropriate and useful.
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On the other hand, many instincts--indeed, probably the greater number--are not perfect, but "imperfect." Imperfect instincts are those which do not fully equip the animal with the function in question, but only take him part way to the goal.