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Sex reversal in Rana pipiens.

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Zoological Laboratory, S t a t e University of Iowa
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.
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.
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
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
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.
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
Posterior two lobes prevailingly testicular
Mature spermatozoa in testicular
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
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.
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.
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.
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.
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.
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sex, reversal, pipiens, rana
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