The introduction of slightly new elements into our manner is attended with benefit; the new can be fused with the old, and the monotony of our action is relieved. But if the new element is too foreign, we cannot fuse the old and new—nature seeming equally to hate too wide a deviation from our ordinary practice, and no deviation at all. Or, in plain English—if any one gives us a new idea which is not too far ahead of us, such an idea is often of great service to us, and may give new life to our work—in fact, we soon go back, unless we more or less frequently come into contact with new ideas, and are capable of understanding and making use of them; if; on the other hand, they are too new, and too little led up to, so that we find them too strange and hard to be able to understand them and adopt them, then they put us out, with every degree of completeness—from simply causing us to fail in this or that particular part, to rendering us incapable of even trying to do our work at all, from pure despair of succeeding. It requires many repetitions to fix an impression firmly; but when it is fixed, we cease to have much recollection of the manner in which it came to be so, or of any single and particular recurrence. Our memory is mainly called into action by force of association and similarity in the surroundings. We want to go on doing what we did when we were last as we are now, and we forget what we did in the meantime. These rules, however, are liable to many exceptions; as for example, that a single and apparently not very extraordinary occurrence may sometimes produce a lasting impression, and be liable to return with sudden force at some distant time, and then to go on returning to us at intervals. Some incidents, in fact, we know not how nor why, dwell with us much longer than others which were apparently quite as noteworthy or perhaps more so. Now I submit that if the above observations are just, and if, also, the offspring, after having become a new and separate personality, yet retains so much of the old identity of which it was once indisputably part, that it remembers what it did when it was part of that identity as soon as it finds itself in circumstances which are calculated to refresh its memory owing to their similarity to certain antecedent ones, then we should expect to find:—