S E X REVERSAL I N RANA PIPIENS' TITUS C. EVANS Zoological Laboratory, S t a t e University of Iowa THREE FIGURES Since the classical work of Spengel ('76) on the urogenital system of amphibians many cases of hermaphroditism in frogs have been examined, both microscopically and genetically. It has been inferred that in certain European frogs there is R definite tendency toward rudimentary hermaphroditism, and that within some species there are local races showing hereditary variations of this tendency. It would seem of interest t o investigate whether analogous conditions exist among some of the American species. At least three cases of hermaphroditism have been reported for Rana catesbiaiia, oiie for R. cantabrigensis, and seven f o r R. pipiens (see bibliography). The latter species especially exhibits a pronounced tendency toward iiitcrsexuality. Last February ( '30), the writer found an additional case which seems worthy of a short description, because both male and female characters are uiiusually well developed and the morphological details of the sex-transf ormiiig regions reveal the homologies of the medullary structures of ovary and testis with unique clarity. DESCRIPTION The specimen is an adult Rana pipieiis of normal size. The length from nose to mius is 6 em. and with the legs extended the total length is 15 em. The external characters are those of a young male. The body is slender ; thumbs and forearms 'Aided by a g r a n t of the Coniiunttee for Research in Problems of Sex of the National Research Council. 47 THE ANATOMIPAS RFCORD. YOL. 4d, XO. 1 48 TITUS C. EVANS a r e slightly larger than female size, though they do not attain the adult male type. The general appearance of the anterior lobes of the gonads is that of y o m g ovaries, but the distinctly testicular character of the posterior end of the left sex gland shows that it is a n ovotestis. Closcr. observation also reveals a small testicul a r region at the posterior tip of the right g o r i d (fig. 1). The left gonad is 12.5 mm. in length; the right one is only 9. The latter is much more folded and ovarial in character. Large fat-bodies a r e present anterior to each ovotcstis and, in addition, a very small fat-body is attached to the testicular portion of the right gonad. The right oviduct is female in appearance, except that the c~onvolutionsa r e fewer in number than in a normal female and the uterine portion is not enlarged. The left oviduct is also of the female type at the anterior region ; but posteriorly from the region where the ovarial lobes of the left gonad merge into the testicular portion, the oviduct is correspondingly of tlic male type. From the testicular region posteriorly to the cloaca the left oviduct is very small and not convoluted. The anterior parts of both oviducts a r e flattened and very inconspicuous. Seminal vesicles are iioticed on the mesonephric ducts posterior to the kidneys. Tlic left ovotestis was sectioned in the sagittal plane. Cross-sections were made of the right gonad, both oviducts, the seminal resicles, and the cloaca. Tlic three anterior lobes of the left gonad and the corresponding fire of the right a r e distiiictly ovarial in character. However, the fact that no ripe eggs a r e present while the larger auxocytes a r e undergoing degeneration proves that oogenesis is already iinder the control of thch testicular parts. Sex traiisformatioii is progressing in the following two segments of each gonad. This has resulted, in the posterior lobe of the left one, in the formation of typical testicular tissues with ripe sperms present in the seminiferous tubules. The most conspicuous feature of the transformatioii process is the redifferentiation of the ovarial rete into the testicular type. Fig. 1 Ventral view of urogenital of left oviduct t o amount of ovary gonad. Organs outlined with aid of posterior ends of mesonephric ducts sections. organs. Note relation of posterior portion replaced by testirular material in the left camera lucida. x 4. Seminal vesicles and and oviducts have been reconstructed from 49 50 TITT'S C . EVAIIC'S The rete of an adult female coiisists of a rudiment of the primordial rctc cord in the hilum, of the ovarial sac, and the cxteriial thecae of the egg follicles (Witschi, '29). The first of these three p a r t s starts to grow out through thc mesogonium until it reaches the inner edge of the mesonepliros (fig. 2, r ) . It still consists of a solid strand of cells in the sexti*ansformiiig segments, while in the posterior testicular seg- Fig. 2 Composite drawing of srwral transrcrse srrtions through the posterior portiou of the riglit gonad aiid nitvoiiephros. Note forni:rtion o f rete material ( T ) and seminiferous tubules (-7). A vas efferens ( v ) extends toward the medial portion of the mesonephros. X 30. SEX BEVEBSAL I N RANA PIPIEKS 51 ments a lumen appears, thus completing the formation of typical vasa efferentia. The walls of the ovarial sacs and the external thecae become more and more solid, and transform into the canal system of the intratesticular rete and the seminiferous tubules (figs. 2 and 3). Fig. 3 Right gonad. Photomicrograph of transverse section through anterior region of the eighth lobe, showing progressive stages of the transformation of orarial follicles into rete tubules ( a to d ) . x 70. Table o f sex characters Primary sex organs LPft side Ziyht szde Anterior three lobes prevailingly ovarial Posterior two lobes prevailingly testicular Mature spermatozoa in testicular region Six rasa efferentia present Anterior six lobes prevailingly ovarial Eighth and part of seventh lobe prevailingly testirular No mature spermatozoa Five vasa eff erentia Secondary sex organs Oviduct female in character Oviduct anteriorly female and posteriorly male O n both sides Seminal vesicles primitive ; thumbs (second digit of fore limb) tending toward maleness 52 TITIJS C. EVANS DISCUSSION There are two possiblc interpretations of the conditioii of bisexuality a s found in this specimen. The first explanation would be that of complete and original hermaphroditism, and the other .would be that of sex reversal. If the specimen had originally contained both male- and f emale-det ermined embryonic cells, the result in the mature frog would have been the co-existence of distinct ovaries and testes. Such is not the case in this specimen. On the contrary, an intermediate region is present in each gonad which shows the transformation stages from ovary to testis. One must then consider the specimen under discussion from the viewpoint of sex reversal. Here again we find an alternative of two possibilities. Is the hermaphrodite a genotypical male which has gone through a female phase or is it a constitutional female changing to the male sex? At the present no definite answer can be offered. However, the large size of the oviducts in this specimen indicates that they grew at one time under ovarial control. A study of the charts and illustrations of Christensen's paper ('30) shows that the ovarial portions in the present condition are not sufficiently developed to haw caused this effect. The fact that the uteri connect through open genital pores with the cloaca seems t o indicate that at one time the animal possessed much larger ovaries and had even functioned as a mature female in egg laying. It may be further taken into consideration that the breeding experiments of Crew ( '21) and Witschi ( '29) with hermaphroditic grass frogs prove that all such cases are genotypical females, for all of the ova and sperms were female-determiiiant. The facts therefore rather favor the assumption that our case is a genetical female (XX), in which sex inversion has been induced by some unknown environmental factor. The writer wishes to express his appreciation to Dr. Emil Witschi for his kind help and interest in this study. SEX REVERSAL IN RANA PIPIENS 53 BIBLIOGRAPHY CHENG,TSO-HSIN 1929 Intersexuality in Rana eantabrigensis. Jour. Morph. and Physiol., vol. 48, p. 345. CHIDESTER,F. E. 1926 Incipient hermaphroditism in the bullfrog. Anat. Rec., vol. 34, p. 142. CHRISTENSEN, KERMIT1929 Hermaphroditism in Rana pipiens. Anat. Rec., 1-01. 43, p. 345. 1930 Sex differentiation and development of oviducts in Rana pipiens. Am. Jour. Anat., rol. 45, p. 159. CLEMENS,W. A. 1921 A case of complete hermaphroditism in the bullfrog (Rana catesbiana). Anat. Rec., vol. 22. CREW,F. A. E. 1921 Sex reversal in frogs and toads. A review of the recorded eases of abnormality of the reproductive system and a n account of a breeding experiment. Jour. Gen., vol. 11, p. 141. KING, H. D. 1910 Some anomalies in the genital organs of Bufo lentiginosus and their probable significance. Am. Jour. Anat., vol. 10, p. 159. MACLEAN, B. L. 1929 Abnormal reproductive organs in a specimen of Rana pipiens. Anat. Rec., vol. 43, p. 53. NEAL,H. V. 1924 A case of unilateral or true gynandromorphism in a leopard frog. Anat. Rec., vol. 29, p. 113. SWIXGLE, W. W. 1917 The accessory chromosome in a frog possessing marked hermaphroditic tendencies. Biol. Bull., vol. 33, p. 70. WITSCHI,EMIL 1921 Der Hermaphroditismus der Frosche, UBW. Arch. Entw., Bd. 49, S. 316. ____ 1923 Uber die genetische Konstitution drr Frosehzwitter. Biol. Zentrabl., Bd. 43, S. 83. 1929 Studies on sex differentiation and sex determination i n amphibians. I. Jour. Exp. Zool., vol. 52, p. 235. 1929 Studies on sex differentiation and sex determination in amphibians. 11. Jour. Exp. Zoijl., vol. 52, p. 267. 1929 Studies on sex differentiation and sex determination i n aniphibians. 111. Jour. Exp. Zool., vol. 54, p. 157.