The relatively clear and simple developmental pattern of the frog gonad (Witschi 1914, 1924, 1929) makes it a good basic type with which to compare the sex glands of higher vertebrates. The origin and development of the elements of the sex glands of higher vertebrates, especially mammals, are not as clear as in amphibia.
Proceedings of the Iowa Academy of Science
©1942 Iowa Academy of Science, Inc.
Thomson, J. D.
"Comparative Studies on Gonad Development in the Rat, the Pig and in Cattle,"
Proceedings of the Iowa Academy of Science, 49(1), 475-501.
Available at: https://scholarworks.uni.edu/pias/vol49/iss1/96