The moods of love, like the more stereotyped manifestations of sex, are dependent upon a proper supply to the blood of the internal secretions of the reproductive organs, the gonadal endocrines. If the testes are removed from frogs, it is found that the clasp-reflex, symptom of sex desire, is abolished. If, after an interval of several days, the testes' extract is injected into the frog, the reflex reappears for a few days. The hormone provoking this sex reflex is present in the testes only during the breeding season. In birds, the seasonal nesting and migrating instincts may be eliminated by interfering with their ovaries. At the same tine there is a change in their plumage toward the male type. Similarly, the males, when their sex endocrines are cut off, will change their psychic nature as well as physically. Besides owning his flag-waving comb, his spurs and brighter feathers, the rooster struts to attract the female, and fights aggressively with his sex competitors. When he is made a capon, he loses his spurs and comb and distinctive plumage, and in addition becomes retiring and submissive, in short, a pseudo-hen in his instincts as well as in appearance. If the genital glands are extirpated from a male before puberty, the wattles remain small, pale and bloodless, no active, amorous or combative instinct emerges. The creature maintains a demure silence, and may even be sought by a virile male. So we may see homosexuality of a kind in the lowest animals. On the other hand, hens deprived of ovaries tend to metamorphose in the male direction, even to acquire the male spurs, and to display the male attitudes. All through the animal world, in the springtime, when the pituitary awakens or increases its secretion, and so stimulates the sex glands to augmented activity, emotions of sex and their expression are provoked by the inner stirring. When the nightingale warbles passionately and the mocking bird gurgles provokingly, when the robin fills its scarlet breast and the starling floats in ecstasy through the perfumed air, when the pigeon coyly woos its mate, and the butterfly flirts with the dazzling multicolors of its wings, when all the marvelous devices of sex attraction in nature, selection and courting, mating and reproducing are pondered, who but must wonder at the infinite possibilities of reaction of the sex hormones? All is for love, and all is because of the love in the blood that is manufactured unconsciously by a few hidden cells. EXPRESSIONISM AND EXHIBITIONISM