him, and to which he goes only to escape the rigors of the northern climate. For several weeks in the spring he goes about the fields, gathering up the worms and grubs. After his long flight from the South he experiences several weeks of an almost ideal existence, his food is plentiful, he becomes strong and hearty, and then he turns to thoughts of love. In the pairing season he does more work than at any other time in the year: fantastic dances, racing and chasing after the females, and savage fights with rivals. He endures more than would be possible in his ordinary physical state. Then come the care of the young and the long flights for water and food during the drought of the summer. After the molt, autumn finds him once more in flock, and with the first frosts he is off again to the South. In the wild state, rut is the capstone of perfect physical condition." (A.W. Johnstone, "The Relation of Menstruation to the other Reproductive Functions," _American Journal of Obstetrics_, vol. xxxii, 1895.) Wiltshire ("Lectures on the Comparative Physiology of Menstruation," _British Medical Journal_, March, 1888) and Westermarck (_History of Human Marriage_, Chapter II) enumerate the pairing season of a number of different animals. With regard to the breeding seasons of monkeys, little seems to be positively known. Heape made special inquiries with reference to the two species whose sexual life he investigated. He was informed that _Semnopithecus entellus_ breeds twice a year, in April and in October. He accepts Aitcheson's statement that the _Macacus rhesus_, in Simla, copulates in October, and adds that in the very different climate of the plains it appears to copulate in May. He concludes that the breeding season varies greatly in dependence on climate, but believes that the breeding season is always preserved, and that it affects the sexual aptitude of the male. He could not make his monkeys copulate during February or March, but is unable to say whether or not sexual intercourse is generally admitted outside the breeding season. He quotes the observation of Breschet that monkeys copulate during pregnancy.