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2. Marshall's Physiology of Reproduction, edit. by Parkes, A. S. (Longmans, Green and Co., Ltd., London, 1960).
3. Bishop, D. W., Sex and Internal Secretions, Chap. 13 (Williams and Wilkins Co., Baltimore, 1961).
4. Rothschild, Proc. Roy. Soc., B, 151, 1 (1959).
5. Baker, J. R., Quart. J. Exp. Physiol., 21, 139 (1931).