During the winter months, ovaries and oviducts of the sparrows are greatly reduced. Injection of pregnant mare serum during this resting period stimulates the ovary to an activity which simulates that of the breeding season. Oviducts respond to the increased amounts of female hormone released by the ovary.
Proceedings of the Iowa Academy of Science
©1936 Iowa Academy of Science, Inc.
Miller, Richard Avery
"The Responses of Normal and Castrate Female Sparrows to Injections of Pregnant Mare Serum,"
Proceedings of the Iowa Academy of Science, 43(1), 395-396.
Available at: https://scholarworks.uni.edu/pias/vol43/iss1/146