Differentiation of the male gonad in the frog, Rana cyanophlyctis (Schneider)

Abstract

With respect to the mode of development and sex-differentiation of the gonads the species of the genus Rana are said to fall into two categories: (A) Gonochoristic and (b) Hermaphroditic. In the former category the gonad develops directly into differentiated testis or ovary from the indifferent stage. In the latter, while in the genetic female the development of ovary is direct, that of the gonad of the genetic male passes through an ovarian phase before differentiating into a definitive testis.The present study was carried out to investigate the mode of development and differentiation of the male gonad in the skipper frog, Rana cyanophlyctis (Schneider). The gonads were studied morphologically and histologically in tadpoles of various developmental stages and in newly metamorphosed froglets. The tadpoles were staginated according to the normal table of Taylor and Kollross (1946) for Rana pipiens. The studies were made on tadpoles during premetamorphic period (stages I-XI), prometamorphic period (stages XII-XVIII), metamorphic climax (stages XIX-XXIV) and in the young froglet (stage XXV). The gonads are in an indifferent phase of differentiation in the premetamorphic tadpoles of stages I-XI. At stage XII the gonads of genetic males and females can be recognized morphologically by their size: the developing ovaries are larger and lobulated while the male gonads are small and narrow strips. Histologically also the two gonads are distinctly different from each other. The male gonad at this stage contains a small number of oocytes and undifferentiated germ cells at the periphery. By stage XIV-XV while the oocytes are still present, a small number of rete cells also appear in the medullary region. Upto stage XVI the germ cells located on the periphery appear to be differentiating into oocytes keeping the gonad in an ovarian phase. At stage XVII-XVIII the peripheral cells are found to form small groups of undifferentiated germ cells. With the emergence of forelimbs and beginning of metamorphic climax, the oocytes start degenerating; the peripheral germ cells migrate towards medullary region where they form groups surrounded by rete cells to form seminiferous tubules. By the end of metamorphosis all the oocytes disappear and the male gonad of the froglet is now a definitive testis. It is concluded that the frog Rana cyanophlyctis belongs to the hermaphroditic category in which the male gonad passes through an ovarian phase during its development and differentiation.