MANY INSTINCTS ARE TRANSITORY.--Not only do instincts ripen by degrees, entering our experience one by one as they are needed, but they drop out when their work is done. Some, like the instinct of self-preservation, are needed our lifetime through, hence they remain to the end. Others, like the play instinct, serve their purpose and disappear or are modified into new forms in a few years, or a few months. The life of the instinct is always as transitory as is the necessity for the activity to which it gives rise. No instinct remains wholly unaltered in man, for it is constantly being made over in the light of each new experience. The instinct of self-preservation is modified by knowledge and experience, so that the defense of the man against threatened danger would be very different from that of the child; yet the instinct to protect oneself in _some_ way remains. On the other hand, the instinct to romp and play is less permanent. It may last into adult life, but few middle-aged or old people care to race about as do children. Their activities are occupied in other lines, and they require less physical exertion. Contrast with these two examples such instincts as sucking, creeping, and crying, which are much more fleeting than the play instinct, even. With dentition comes another mode of eating, and sucking is no more serviceable. Walking is a better mode of locomotion than creeping, so the instinct to creep soon dies. Speech is found a better way than crying to attract attention to distress, so this instinct drops out. Many of our instincts not only would fail to be serviceable in our later lives, but would be positively in the way. Each serves its day, and then passes over into so modified a form as not to be recognized, or else drops out of sight altogether. SEEMINGLY USELESS INSTINCTS.--Indeed it is difficult to see that some instincts serve a useful purpose at any time. The pugnacity and greediness of childhood, its foolish fears, the bashfulness of youth--these seem to be either useless or detrimental to development. In order to understand the workings of instinct, however, we must remember that it looks in two directions; into the future for its application, and into the past for its explanation. We should not be surprised if the experiences of a long past have left behind some tendencies which are not very useful under the vastly different conditions of today. Nor should we be too sure that an activity whose precise function in relation to development we cannot discover has no use at all. Each instinct must be considered not alone in the light of what it means to its possessor today, but of what it means to all his future development. The tail of a polliwog seems a very useless appendage so far as the adult frog is concerned, yet if the polliwog's tail is cut off a perfect frog never develops.