An objection suggests itself that if such a habit as the flight of birds, which seems to require a little personal supervision and instruction before it is acquired perfectly, were really due to memory, the need of instruction would after a time cease, inasmuch as the creature would remember its past method of procedure, and would thus come to need no more teaching. The answer lies in the fact, that if a creature gets to depend upon teaching and personal help for any matter, its memory will make it look for such help on each repetition of the action; so we see that no man’s memory will exert itself much until he is thrown upon memory as his only resource. We may read a page of a book a hundred times, but we do not remember it by heart unless we have either cultivated our powers of learning to repeat, or have taken pains to learn this particular page. And whether we read from a book, or whether we repeat by heart, the repetition is still due to memory; only in the one case the memory is exerted to recall something which one saw only half a second ago, and in the other, to recall something not seen for a much longer period. So I imagine an instinct or habit may be called an inherited habit, and assigned to memory, even though the memory dates, not from the performance of the action by the learner when he was actually part of the personality of the teacher, but rather from a performance witnessed by, or explained by the teacher to, the pupil at a period subsequent to birth. In either case the habit is inherited in the sense of being acquired in one generation, and transmitted with such modifications as genius and experience may have suggested.