1. Chitty, H., and Austin, C. R., Nature, 179, 592 (1957).
2. Chitty, H., J. Endocrinol., 15, 279 (1957).
3. Hoyte, H. M. D., J. Animal Ecol., 24, 412 (1955).
4. Asdell, S. A., Patterns of Mammalian Reproduction, second ed. (Cornell University Press, Ithaca, 1964).
5. Delost, P., Arch. Anat. Microsc. Morph. Exp., 44, 150 (1955).