[92] W. Heape, "The Menstruation of _Semnopithecus Entellus_," _Philosophical Transactions_, 1894; "Menstruation and Ovulation of _Macacus Rhesus_," _Philosophical Transactions_, 1897. [93] W.L. Distant, "Notes on the Chacma Baboon," _Zoölogist_, January, 1897, p, 29. [94] _Nature_, March 23, 1899. [95] W. Heape, "The Menstruation of _Semnopithecus Entellus_," _Philosophical Transactions_, 1894, p. 483; Bland Sutton, _Surgical Diseases of the Ovaries_, 1896. [96] T. Bryce and J. Teacher (_Contributions to the Study of the Early Development of the Human Ovum_, 1908), putting the matter somewhat differently, regard menstruation as a cyclical process, providing for the maintenance of the endometrium in a suitable condition of immaturity for the production of the decidua of pregnancy, which they believe may take place at any time of the month, though most favorably shortly before or after a menstrual period which has been accompanied by ovulation. [97] Robinson, _American Gynecological and Obstetrical Journal_, August, 1905. [98] Bossi, _Annali di Ostetrica e Ginecologia_, September, 1896; summarized in the _British Medical Journal_, October 31, 1896. As regards the more normal influence of the ovaries over the uterus, see e.g. Carmichael and F.H.A. Marshall, "Correlation of the Ovarian and Uterine Functions," _Proceedings Royal Society_, vol. 79, Series B, 1907. [99] Beuttner, _Centralblatt für Gynäkologie_, No. 49, 1893; summarized in _British Medical Journal_, December, 1893. Many cases show that pregnancy may occur in the absence of menstruation. See, e.g., _Nouvelles Archives d'Obstétrique et de Gynécologie_, 25 Janvier, 1894, supplement, p. 9. [100] It is still possible, and even probable, that the primordial cause of both phenomena is the same. Heape (_Transactions Obstetrical Society of London_, 1898, vol. xl, p. 161) argues that both menstruation and ovulation are closely connected with and influenced by congestion, and that in the primitive condition they are largely due to the same cause. This primary cause he is inclined to regard as a ferment, due to a change in the constitution of the blood brought about by climatic influences and food, which he proposes to call gonadin. (W. Heape, _Proceedings of Royal Society_, 1905, vol. B. 76, p. 266.) Marshall, who has found that in the ferret and other animals, ovulation may be dependent upon copulation, also considers that ovulation and menstruation, though connected and able to react on each other, may both be dependent upon a common cause; he finds that in bitches and rats heat can be produced by injection of extract from ovaries in the oestrous state (F.H.A. Marshall, _Philosophical Transactions_, 1903, vol. B. 196; also Marshall and Jolly, id., 1905, B. 198). Cf. C.J. Bond, "An Inquiry Into Some Points in Uterine and Ovarian Physiology and Pathology in Rabbits," _British Medical Journal_, July 21, 1906.