Effect of Castration on the Oviduct in Males and Females of Rana pipiens. ∗

Abstract

Rana pipiens is unique among all frog species for the surprisingly well developed oviducts in the male, although in the male they do not undergo the cyclical changes so characteristic of the female. From anterior to posterior, 4 parts are differentiated in the oviduct: a funnel opening, the ostium tubae; then a short, straight tube, the pars recta; a convoluted, glandular portion, the pars convoluta; and lastly, the uterus. The anterior parts of the oviducts of the male are less developed than the posterior parts. This difference distinguishes the oviducts of the male from those of the female.

Oviducts have been found in male toads and in hermaphroditic frogs and toads 1 , 2 but in these cases, the existence of the oviduct is clearly dependent upon some development of ovarial structures. This was suggestive therefore of an investigation to discover if the unusual growth of the oviducts in the male leopard frog also is correlated with hermaphroditic tendencies in the development of the male gonad. The embryological study showed, however, that as a rule the testes are typically differentiated before the time of metamorphosis which may even be before the first appearance of the primordia of the oviduct.

The oviducts in young frogs, both males and females, are similar in their gross structure except for the slightly larger size in the females. In microscopic sections, the size variance is somewhat more evident. In second year frogs, the sex differences in the oviducts are rather striking.

It appears then that 2 phases exist: (1) a period of self-differentiation in both sexes, and (2) in the female only, a period under the control of the ovary in which the oviducts enlarge to their final size and become functional. In the male, further development stops.