Marvelous are all the manifestations of the reproductive necessity. Considering that reproduction was at first merely a form of growth, a discontinuous kind of growth, that seized upon sex as a splendid means to escape death, the chemical methods evolved arouse a sense of awe. A baby is born with her or his glands practically as fixed for her or him as the color of the eyes. Thymus and pineal keep him a child, keep him unsexed. Then at puberty, a new current is added to the calmly flowing river, and behold! a turmoil. Ovaries or testes actively functioning erupt upon the calm spectacle, and the girl is transfigured into the maid, the boy into the youth. After the ovaries, the corpus luteum: after the corpus luteum, the placenta: after the placenta, the mammary glands: after that the cycle begins again until the ovaries are exhausted and the chain is broken. Besides, all the other glands of internal secretion beat in rhythm, fluctuate in their activities, may divide prematurely the tides or dam them completely. Innumerable varieties and combinations of interglandular action supply us with the limitless types of adolescent girls. Some endocrine cooperatives that make one girl stable and settled, will make others unstable and unsettled. Alicia may be hyperthyroid, and so excitable, nervous, restless, and subject to palpitation of heart and sleeplessness. Bettina may have too much post-pituitary, and so will menstruate early, tend to be short, blush easily, be sentimentally suggestive and sexually accessible. Christina may be adrenal cortex centred and so masculinoid: courageous, sporty, mannish in her tastes, aggressive toward her companions. Dorothea may have a balanced thyroid and pituitary and so lead the class as good-looking, studious, bright, serene and mature. Florence, who has rather more thyroid than her pituitary can balance, will be bright but flighty, gay but moody, energetic, but not as persevering. And so on and so on. Environment, habit-formation, training, education serve only to bring out the internal secretion make-up of the girl, or to suppress and distort and so spoil her. Adolescence will be peaceful, calm, semi-conscious, or disturbing, revolutionary and obsessive according to the reaction of the other endocrines to the rise of the ovaries. Harmony, and so continued happiness of the mind and body, means that they have been welcomed into the fold. Disharmony, ailments, unhappiness, difficulties, mean that they are being treated as intruders, or are acting as marauders. The after life, sexually the period of maturity, barring accidents, diseases, and shocks, will bear the same character. The kind of adolescence provides the clue to the kind of maturity, for both are effects of the same endocrine factors. THE SEX GLAND CHAIN