These accessory sex-serving traits undoubtedly survived because of their usefulness in external adornment for attracting attention in courtship, in the metabolic requirements of sex combat and the sex act, and in the necessities of caring for the young, until well-grown. The rooster's comb and spurs, the male frog's claspers, the stag's antlers, and so on, are familiarly and obviously so useful. Besides there are fundamental differences in inner physiology. The human male consumes more oxygen than the female per minute, since he has more red corpuscles in his blood. In some caterpillars the blood is yellow in the males and green in the females. W.I. Thomas has devoted an essay of some fifty pages to a review of the organic differences between man and woman. The ordinary criteria, employed every day by the man in the street to distinguish man from woman may be arranged as follows: _Man_ _Woman_ Hair on face Hairless face Skin coarse and lean Skin fine and plump Muscles powerful Relatively weak Bones heavy Bones light Aggressive--bass voice Reserved--treble voice THE RÔLE OF THE OVARIES While the primary sex characters, as such, are present and distinguishable from birth, quite the opposite holds for the secondary sex traits. During childhood they are in abeyance or at least pretty sharply suppressed. Girls and boys who are permitted to dress alike, to play the same games and among whom no consciousness of sex is encouraged are often difficult to tell apart. The boys will be boys, and most of the girls tom-boys. With puberty comes a marked change of attitude toward the other sex. Puberty is the time of ripening of the specific germ cells. It is then the ovaries begin to secrete ova ripe for fertilization, and the testes begin to secrete sperm ready to fertilize. Before this can happen an event announced in the female by the onset of menstruation, two conditions must be fulfilled in the endocrine history of the individual. There must be a certain atrophy and retrogression of the thymus gland, and there must likewise be a similar atrophy and retirement of the pineal gland. Both of these involutions of the glands of childhood must occur before the normal hypertrophy and development of the sex glands and their secretions can start. Besides, there must be a minimum activity of the thyroid, adrenal and pituitary glands. Without them, below a certain minimum, the reproductive organs and their secretions will remain infantile, causing a persistent infantilism or delay of puberty.