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Sex differentiation in triploid newts (Triturus viridescens).

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SEX DIFFERENTIATION I N TR,IPLOID NEWTS
(TRITURUS VIRIDESCENS)
GERHARD FANKHAUSER
Department of Biology, Princeton Unzversity, Princeton, N e w Jersey
THREE TEXT FIGURES AND THREE PLATES (THIRTY-FIVE FIGURES)
INTRODUCTION
Triploid larvae of the newt, Triturus viridescens, occur
occasionally in nature. Since these exceptional individuals
can be identified in life, by chromosome counts in amputated
tail tips, it is possible to follow their development in the
laboratory and to investigate the effects of the increase in
chromosome number.
During the winter 1937-1938, four triploid larvae of Triturus viridescens were raised in the laboratory and preserved
during or immediately after metamorphosis (Fankhauser,
'38b). I n other species of newts, sex differentiation has been
shown to take place shortly before metamorphosis; the condition of the gonads of the four triploids is therefore particularly important, since it should tell us whether o r not the presence
of a third set of chromosomes interferes with the normal
process of sex determination, as it does in insects and in
some dioecious plants. This approach to the study of the
mechanism of sex determination in amphibia is all the more
desirable, because conclusive cvtological evidence is lacking
and breeding experiments with hermaphroditic frogs and
sex-reversed toads have given contradictory results.
The observations on the gonads of the four triploids have
been briefly summarized in a preliminary note ( '3%). A
detailed account will be given in the present paper. Inasmuch
as the normal process of sex differentiation in this species
has not been fully described before, the normal development
227
228
GERHARD FANKI-IAUSER
of the gonads, from the first beginning of differentiation to
metamorphosis, will be considered first. This account is based
on the unpublished investigations of hIr. L. D. Fenninger
( '38).
The appearance of the four triploid animals at the time of
fixation has been described previously ( '38b). They were
preserved in Michaelis' fluid and sectioned at 15 micra, from
the base of the tail forward. I n this way the sections become
so oriented that the left side of the animal appears to the
left in all the photographs. The sections were stained with
Harris ' acid haemalum and Orange G. The photomicrographs
were taken with a Zeiss planachromate 40X and a 5X compensating ocular. In reproduction, the magnification was reduced
to 220X (plate 1) and 198X (plates 2 and 3).
T H E NORMAL PROCESS O F SEX DIFFERENTIATION
The normal development of the gonads follows closely the
descriptions given for other species of salamanders by Abramowicz ( '13, Triton taeniatus), Burns ( '25, Amblystoma punctatum), and &Curdy ( '31, Triturus torosus). Before the
age of 11 weeks (at 20" to 22OC.), the gonads are small and
undifferentiated, similar to those shown in figure 4. All
the germ cells have large, lightly staining, and irregularly
lobed nuclei. I n some of the 11-week-old larvae, groups of
small, more or less spherical nuclei appear (fig. 5). These
nuclei are the first indication of differentiation in female direction, because spherical nuclei of various structural types
are typical for oogonia and oocytes in later stages and completely absent in young testes (figs. 13 and 16).
At the age of 1 2 weeks, the gonads clearly fall into two
classes. In one group, all the germ cells still possess the polymorphic nuclei that are characteristic for the undifferentiated
gonad (fig. 6). In the other class, the oval or spherical nuclei
have increased in number and, to some extent, in size (fig. 7 ) ,
but show a similar reticular structure as before.
In 13-week-old animals, the young ovaries (fig. 9) are still
more definitely characterized by the presence of a small cavity
SEX I N TRIPLOID SALAMANDERS
229
in some of the sections, and by the appearance of larger
spherical nuclei with the typical " spireme-like " structure
described particularly by Burns. These cells probably are
small oocytes in early stages of the prophase of meiosis (Rodgers and Risley, '38, p. 124). The nuclei of young oocytes
in the early growth period show a similar structure (figs. 14,
15, 17, 18), and similar cells have been described as oocytes
in ovaries of adult salamanders (Pischer, '35). The other
type of gonads, presumably young testes, resembles closely
undifferentiated gonads, until the beginning of metamorphosis
(figs. 8 and 10).
I n larvae 14 weeks old, the gonads are considerably larger
(figs. 10 to 12). I n the ovaries, the cavity is clearly marked,
and the small oocytes have increased in size and number.
Undifferentiated germ cells, with pale, irregularly lobed nuclei, are still present and persist through metamorphosis
(fig. 17). Similar cells are also found in the wall of mature
ovaries.
At the beginning of metamorphosis (about 16 weeks from
fertilization), the ovaries contain growing oocytes which begin to bulge out into the cavity (figs. 14 and 15). At the
periphery, nests of germ cells (oogonia and, predominantly,
very young oocytes) are present. The testes are solid structures, with germ cells scattered throughout the cross section
(fig. 13). The nuclei of these spermatogonia are still polymorphic, but in the majority of the nuclei the lobes are
broader and more rounded in contrast to the narrower, more
pointed lobes of the undifferentiated germ cells (figs. 20 and
21). This change in the shape of the nuclei of the germ cells
seems to be the first distinguishing feature between undifferentiated gonad and testis.
Toward the end of metamorphosis (about 18 weeks from
fertilization), the testis still presents a similar picture (fig.
16), while the ovary has grown considerably (figs. 17 and 18).
This increase in size is connected primarily with growth of
230
GERHARD F A N K H A U S E R
the larger oocytes which almost completely obliterate the
ovarian cavity.
A t the time of metamorphosis, ovary and testis are therefore clearly differentiated by the following features (cf.
Burns, '25) :
The ovary possesses a small central cavity, nests of oogonia
and small oocytes wit11 spherical nuclei at the periphery, and
growing oocytes protruding into the central cavity; undifferentiated germ cells with polymorphic nuclei are still present
in considerable number. The testis is a solid structure, with
germ cells distributed throughout the cross section. All the
germ cells (spermatogonia) have broadly lobed nuclei which
differ slightly from the polymorphic nuclei of undifferentiated
germ cells.
Reconstructions show that the testes are shorter than the
ovaries (ca. 950 to 1000 micra against 1650 to 2450 micra, figs.
1 to 3 ) . Their anterior end is usually located near the tenth
spinal ganglion, while the ovaries may extend beyond the ninth
ganglion. The left ovary is frequently shorter than the right,
but may be wider and slightly more advanced in its differentiation.
THE GONADS OF' THE FOUR TRIPLOIDS
The youngest triploid (no. 20) was fixed at the age of 153
weeks, shortly after the beginning of metamorphosis. The
gonads a r e typical testes, normal in every respect, as the
comparison of figures 19 with 13 and 16 shows. Graphic reconstructions (fig. 1)demonstrate that the testes a r e of about
the same length as in the conti*ols, but slightly wider.
The second triploid (no. 5 ) was fixed toward the end of
metamorphosis, a t the age of 17 weeks. Three representative
sections through the gonads are shown in figures 25 to 27.
A cornparison with corresponding sections through the ovaries
of a control (figs. 22 to 24) at once demonstrates that the gonads
of the triploid a r e ovaries ; a small central cavity is present,
and germ cells with spherical nuclei (young oocytes) are
visible in figures 25 and 27. However, the undifferentiated
SEX I N TRIPLOID SALAMANDERS
231
germ cells with polymorphic nuclei predominate (fig.26), and
the cross section of the ovary as a whole is definitely smaller
than normal. The last-mentioned difference is also clearly
brought out by reconstructions (fig. 2).
The gonads of the third and fourth triploids (nos. 10 and
ll), fixed at the age of 18 weeks, present a similar picture
DI PLOlD
DIPLOID
TRIPLOID
Fig. 1 Reconstructions of testes of three animals in metamorphosis. A,
diploid no. 4, 16 weeks. B, diploid no. 6, 18 weeks. C, triploid no. 20, 15.4 weeks.
A
DIPLOID
I
B
DIPLOID
C
TRIPLOID
Fig. 2 Beconstructions of ovaries. A, diploid no. 1, 173 weeks. B, diploid
no. 13, 16 weeks. C, triploid no. 5, 1 7 weeks.
232
GERHARD FANKHAUSEE
(figs. 30 to 32, and 36 to 38). The gonads are rudimentary
ovaries, with a central cavity and a small number of young
oocytes. The undifferentiated germ cells are more numerous,
particularly in the left gonad of the fourth triploid (figs. 36
to 38). Oocytes in early growth stages are entirely absent. The
reconstructions of figure 3 also demonstrate the reduced size
of the triploid ovaries.
C
DIPLOID
TRIPLOID
TRIPLOID
Fig. 3 Reconstructions of ovaries. A, diploid no. 12, 18 weeks. 13, triploid
no. 10, 18 weeks. C, triploid no. 11, 18 weeks.
A more accurate basis for comparisons is given by the
actual number of germ cells present in the ovaries of different animals. The various types of germ cells were counted
in the left ovary of the triploid no. 5 (figs. 2C and 25) and of
three diploid animals, 11,14 and 174 weeks old (figs. 5 , 1 2 and
22). Table 1 shows that the total number of germ cells in
the triploid ovary is only about one-third of the normal number. Cells with spherical nuclei are still in the minority and
should probably be classified as very young oocytes, while
233
SEX I N TRIPLOID SALAMANDERS
in the control small oocytes with typical prophase nuclei are
predominant.
A more detailed investigation would be necessary to establish with certainty the significance of all the different
TABLE 1
N u m b e r of undifferentiated g e r m cells, oogonia, and oocytes in left ovary of
t w o larvae and t w o animals a t end o f metamorphosis
TYPD O F NUCLEUS
TYPE O F QERM
IARVA
CELLS
11 WE.FXB
Small, lobed (found at
posterior end of goundifferentiated
nads only)
Large, lightly stained,
irregularly lobed
undifferentiated
(polymorphic)
Small, oval or spherical, with reticular
oogonia
structure
S m a 11 t o medium.
spherical, chromatin
in tightly massed
threads (poor fixation of leptotene
and zygotene stages
of meiosis?)
very young oocytes
M e d i u m , spherical,
Rith prohase structure (probably earIy pachytene)
young ooeytes
Larger, spherical, with
more diffuse chro- oocytes i n early
growth stage
mosomm
Mitoses
Degenerating nuclei
Total
DIPLOID
NO. 1
71 WEEKL
TRIPLOID
NO. 5
17 WEEKS
18
-
-
100
206
132
249
-
-
186
5G
69
106
315
1
9
11
1
-
LARVA
4 WEEKS
3
149
-
4
4
671
593
206
types of germ cells that are present in the young ovary. However, a comparison of the numbers of different cell types found
in the left ovary of the three diploid animals of different ages
suggests strongly that the cells with spherical nuclei and
234
GERH.4RD FANKHAUSER
massed chromatin threads represent an intermediate stage
between the two adjacent types ; probably they are oocytes in
the earliest stages of meiotic prophase.
DISCUSSION
Of the four metamorphosed, triploid newts examined, one
contains normal testes, while the other three possess rudimentary ovaries. Although there is some variation in the
condition of the ovaries in the three cases, their appearance is
still sufficiently uniform to be characteristic for the triploid
females. Triploidy, therefore, affects the female sex only,
while the male sex appears to be normal.
In animals with a definite sex chromosome mechanism,
triploidy has no effect on the homogametic sex which normally
possesses two X-chromosomes, while the heterogametic sex,
with a single X-chromosome in the diploid complement, is
changed to an intersexual condition. I n Drosophila and Carausius, triploid females are therefore normal, but no normal
triploid males are produced. I n moths, on the other hand,
triploid individuals are either normal males or intersexes,
because the female sex is heterogametic (Bridges, '21; GoldSchmidt and Pariser, '23; see also Vandel, '37).
I n triploid newts, it is also the female sex that is affected.
However, it would be premature t o conclude from this that
newts actually have the same type of sex determination as
moths. It is impossible t o determine whether the presence of
rudimentary ovaries in three of the four triploids indicates
intersexuality, or merely a retardation in the development
of the gonads, caused perhaps by some general, physiological
effects of triploidy. I t should be mentioned, however, that
the triploid intersexes produced by back-crossing hybrids
between different species of moths are all characterized by
rudimentary ovaries, although they vary greatly in the appearance of the other sexual characters (cf. Goldschmidt, '31).
Cytologically, sex chromosomes have not been demonstrated
conclusively in any amphibian, so far. I n Triton palmatus, a
SEX I N T R I P L O I D S A L A M A N D E R S
235
detailed study of the morphology of individual chromosomes
during cleavage revealed the existence of a slightly heteromorphic pair in three eggs out of thirteen (Fankhauser,
’34). There is no definite indication, however, that this pair
represents sex chromosomes.
Breeding experiments with liermaphroditic frogs appear
to demonstrate male heterogamety (Crew, ’21 ; TVitschi, ’23,
’29). I n accordance with these observations, the diploid parthenogenetic frogs that can be reared through metamorphosis
would all be expected to be females. I n recent experiments
with Rana nigromaculata and Rana japonica, Kawamura
( ’39) found, among twenty-three parthenogenetic young frogs,
fifteen typical females, three individuals with abnormal or
degenerating ovaries, two which were “almost transformed
into males,” two with rudimentary testes, and one male. According to his interpretation, the individuals with testes are
genetic females that have undergone sex reversal, caused
perhaps by abnormalities in other organs. A similar explanation was suggested by Parmenter (’25) for the occurrence of
males in Loeb’s material, although in these cases over-ripeness of the eggs is indicated as the possible cause of sex
reversal.
The results of breeding experiments with sex-reversed male
toads are also not entirely conclusive. Harms (’26) obtained
both males and females, while Ponse (’31) found exclusively
males, among 400 individuals from several batches of eggs,
a fact which suggests a homogametic condition of the male.
It is possible, of course, that frogs and toads possess different sex chromosome mechanisms, just as male and female
heterogamety may be found in closely related species of fishes.
Under these circumstances it would be interesting to study
the effects of triploidy on sex in anurans. Kawamura (’39)
reported one case of probable triploidy among his parthenogenetic frogs. The gonads of this individual are rudimentary
testes. If the triploid condition of this animal is confirmed,
the case would offer good evidence for the suggestion that
236
GERHARD F A N K H A U S E R
irogs and salamanders may differ in their sex chromosome
mechanism.
Still more recently, an unexpected confirmation of the observations reported in this paper was received from Sweden.
I n the course of an investigation of spermatogenesis in Triton
taeniatus, Book ( '40) found an individual with triploid testes.
The testes and the other reproductive organs were entirely
normal in appearance. The remaining parts of the animal
had not been preserved but were presumably also triploid.
This discovery of a sexually mature triploid male supports
the conclusion presented here that the effect of triploidy on
sex is not the same in newts as it is in Drosophila. This seems
at first disconcerting in view of the fact that the only haploid
newt that has so far been raised beyond the stage of sex
differentation proved to be a female (Fankhauser, '38a).
The femaleness of this haploid Triton taeniatus appeared
to be in perfect agreement with the expected, and partly observed, consequences of haploidy in Drosophila and suggested
the existence of a similar sex chromosome mechanism in both
animals. It is, of course, not certain that the mechanism in
amphibians conforms exactly t o either one of the two modes
of sex determination found among insects. Unfortunately,
the investigation of this mechanism is greatly complicated
by the fact that, in amphibians, genetic sex determination is
relatively labile and may be influenced or even reversed by
various secondary factors.
For a more satisfactory analysis of the effects of triploidy
on sex in salamanders it will be essential to have a large
number of triploid animals available, and to raise them to a
stage where the reproductive organs of the male and female
are more clearly differentiated. Both of these requirements
have now been fulfilled. On the one hand, it is possbile to induce triploidy in Triturus viridescens by cold treatment of
unsegmented eggs (Fankhauser and Griffiths, '39 ; Griffiths,
'40). On the other, a rather high natural frequency of tri-
SEX I N TRIPLOID SALAMANDERS
237
ploidy was discovered among larvae of the two-lined salamander, Eurycea bislineata, which can easily be raised to a
more advanced stage ( Fankhauser, '39). The condition of
the gonads in these two new groups of triploids is under
investigation at present. The observations made so far appear
to confirm entirely the results reported here.
SUBIMARY
1. The normal process of sex differentiation in Triturus
viridescens is described briefly. At the time of metamorphosis,
ovaries and testes are clearly differentiated. The ovaries
possess a small central cavity, groups of germ cells (oogonia
and very young oocytes) at the periphery, and larger oocytes
which protrude into the central cavity. The oogonia and
oocytes are characterized by the spherical shape and the strncture of their nuclei. Undifferentiated germ cells with polymorphic nuclei arp also present. The testis lacks a cavity, the
spermatogonia are scattered uniformly throughout the cross
section of the gonad and have polymorphic nuclei with broad,
rounded lobes.
2. Four triploid larvae were raised in 1937-1938 and preserved during o r after metamorphosis. The gonads were examined in serial sections through the whole animals. The
gonads of one triploid are typical testes, those of the other
three are rudimentary ovaries which contain less than onehalf the normal number of germ cells, with undifferentiated
germ cells in the majority.
3. I n newts, triploidy therefore affects the female sex only.
Whether the rudimentary conditions of the ovaries of the
triploids indicates intersexuality, corresponding to that found
in triploid moths, or merely a marked delay in growth and
differentiation of the ovaries, caused by general physiological
effects of triploidy, cannot he decided until more and older
triploid individuals have been studied.
238
GERHARD FANKHAUSER
LITERATURE CITED
H. 1913 Die Entwicklung der Goaadenanlage und Elitstellung
ABRAMOWICZ,
der Gonocyten bei Triton taeniatus (Schneid.) Morphol. Jahrb., Bd.
47, S. 593-644.
.
1940 Triploidy in Triton taeniatus Laur. Hcreditas, vol. 26, pp.
107-1 14.
BRIDGES,
C. B. 1921 Triploid intersexes in Drosophila rnelanogast~r. Science,
VOI. 54, 252-254.
BCRNS,R. K. 1925 The sex of parabiotic twins i n Amphibia. J. Exp. Zool.,
v01. 42, PP. 31-89.
CREV-, F. A . E. 1921 Sex-reversal in frogs and toadq. J. Genetics, vol. 11,
pp. 141-181.
F m m i A u s E R , 0. 1934 Cytological studies on egg fragments of the salamauder
Triton. V. J. Exp. Zool., vol. 68, pp. 1-57.
1938a Sex diff ereiitiation i n n haploid salamander, Triton taeniatus Law. J. Exp. Zool., vol. 79, pp. 35-49.
-- 1938b Triploidy in the newt, Triturus viridescens. Proc. Am.
Philos. SO~.,
vol. 79, pp. 715-739.
--___
1938c Sex differentiation in triploid salamanders (Triturus viridescens). Anat. Rec., vol. 72, supal., 11. 70.
1!;39 Polyploidy in the salamander, Eurycca bislincnta. J. Hered.,
TO^. 30, pp. 379-388.
FANKITAUSER,
G., AND K. B. GRIFFITHS 1939 Induction of triploidy and haploidy
in the newt, Triturus viridescens, by cold treatment of unsegmented
eggs. Proc. Nat. Acad. Sci., vol. 25, pp. 233-238.
FENNINGER,
L. I). 1938 Sex differentiation in Triturus viridescens. Senior
Thesis, Princeton University.
FISCHER,
ILSE 1935 Zur Keimbahnfrage bei den urodelen Amphibien. Z. f. mikr.
anat. Forsch., Bd. 37, S. 219-244.
BOOK, J. A .
GOLDsCHMIwr,
It. 1931 Die sexuellen Zwisclienstufen, S. 127-166.
Springer,
Eerlin.
GOLDSCHMIDT, B., AND K. PARISER1923 Triploide Intersexe bei Schmetterlingen. Biol. Zbl., Ed. 43, S. 446-452.
GRIFFITHS, R. E. 1940 Triploidy i n Triturus viridescens, induced by exposure
of eggs to low temperature. Anat. Ree., rol. 76, suppl. 2, pp. 26-27.
IIARMS,J. W. 1926 Beobachtungen iibrr Geschlechtsuruwandlungen rcifer Tiere
und deren F 1 Generation. Zool. Am., Bd. 67, S. G7-79.
KAWA~SUBA,
T. 1939 Artificial !)arthenogenesis in the frog. 11. The sex of
parthenogenetic frogs. J. Sci. Hirosiina Cniv., ser. B, div. 1, vol. 7,
pp. 39-86.
NCCURDT,H. M. 1931 Deielopment of the ?ex organs in Triturus torosus. Am.
J. Anat., rol. 47, pp. 367-403.
SEX IN T R I P L O I D S A L A M A N D E R S
239
PARMIENTER,
C. L. 192.5 The chromosomes of parthenogenetic frogs and tadpoles. J. Gen. Physiol., vol. 8, pp. 1-20.
PONSE,K. 1930 L e problhme du sexe et 1’6volution de l’organe de Bidder
du Crapaud. Proc. 2nd Internat. Congr. Sex Research, pp. 202-210.
RODGERS,
L. T., AND P. L. RISLEY 1938 Sexual differentiation of uriiiogenital
ducts of Amblystoina tigrinuni. J. Morph., vol. 63, pp. 119-141.
VANDEL,A. 1937 Chromosome number, polyploidy, and Bex i n the animal
kingdom. Proc. Zool. Soc., London, vol. 107A, pp. 519-542.
WITSCHI, E. 1923 Ueber die genetisclie Konstitution der Frosclizwitter. Biol.
Zbl., Bd. 43, S. 83-96.
1929 Studies o n sex differentiation and sex deixrmination in
amphibians. 111. J. E X ~ZOO~.,
.
vol. 54, pp. 157-223.
PLATE 1
EXPLANATION OF FIQURES
All figures on plates 1 to 3 are photomicrographs of transverse sections
through gonads. The figures on plate 1a r e magnified 220 X, those on plates 2 and 3
198 x, with the exception of figures 20 and 21 which are magnified 396 X .
4 Eleven weeks. Undifferentiated gonads. Germ cells have lightly stained, polymorphic nuclei.
5 Eleven weeks. First indication of female differentiation : appearance of small,
spherical nuclei with reticular structure (oogonia ).
6 Twelve weeks. Undifferentiated gonads (testes?). Germ cells a s in figure 4.
7 Twelve weeks. Ovaries. Larger, oval or sphcrical nuclei with reticular structure (oogonia).
8 Thirteen weeks. Undifferentiated gonads (testes?). Increase in number of
germ cells.
9 Thirteen weeks. Ovaries. Appearance of small cavities. A t periphery, larger
germ cells with splierical nuclei (young oocytes i n early prophase of meiosis).
10 Fourteen weeks. Testis. Germ cells of same type a s in undifferentiated gonad.
11 Fourteen weeks. Left ovary. Two larger oocytes with spherical and more
lightly staining nuclei a r e visible, also two undifferentiated germ cells with pale,
polymorphic nuclei. Central cavity larger.
12 Fourteen weeks. Left ovary of another larva. Similar to figure 11.
240
241
PLATE 2
EAPLANATION O F FIGURES
.
13 Sixteen \t eeks (beginniiig of ~r~etamoipliosis)Left testis. Speriiiatogoiiia
nitli po1~inorphicnuclei. Lobes of nuclei ;lie broader ant1 niore rounded thau in uniliEcicntiated germ cells (cf. figs. 20 and Zlj.
14 Sixteen weeks. L e f t ovary. THO larger ooavtrs near center. Groul) of w r y
> oung oocytes t o left.
1.5 Ssiiie ovary. Larger oocyte in center, groulis of \cry young oorytcq abore
and t o riglit. To left, three germ cells with polymorphic nuclei.
16 Eighteen weeks (end of iiietaiiiorpliosis). Left testis. Siinilxr t o figure 13.
1 7 aiid 18 Eighteen weeks. Left ovary, iriucli larger than in figures 14 and 15.
Growing oocgtes are protrudiiig iiito c e n t r d cavity. I n figure 17, larger g r o u p
of rerv young oovytes t o right arid i n upper left Iiand corner. T'ndifferentiatecl
g e r m cells with pol? niorphic nuclei :ire still 1)rescnt.
I 9 Triploid no. 20, 16 weeks. I d t gon:cd. T)pical testis.
20 Single undifferentiated gerni cell froiii figure 6, enlarged to shon p l y nroryhic nucleus with irregular, narrow, mid inore or l e ~ spointed lobes.
21 Three sl)erniatogonia f i o n i figure 7 3, twlarged to slim, hroader, inore
rounded lobes of nuclei.
22 t o 24 Diploid 1 1 0 1, 1 7 3 wreks (control for triploid no. 5 ) . 22, left ovaiy,
23 and 24, right o\:iry.
2 3 to 2T Tri1)loitl no. 5, 1 7 weeks. 23, left ovniy, 26 and 2 7 , light o v a q . Note
S l l i U l l size of ovary, sinall nuinher of young oocytrs, and sbsencu of lnrger
oocytes. M:my sections slioxv untliffereiitiated gei in cells with polymorphic nuclei
oiily, as ill figure 26.
REX IN TRIPLOID SAIL\~\LYSI)ERS
PLATE 2
GERHARD FANI<€I.AUSER
243
€'LATIC 3
EXPLANATION O F F I G U R E S
28 and 29 1Xploid no. 12, 18 Hceks (czontrol for triploids no. 10 aiitl no 11).
Left oTarv.
JO to 3 2 TrilJloid no. 10, 18 ueelts. 30 aiid 31, left ovary. 32, right ovary.
Siiiiilar t o figuies 25 t o 27. ~ i i i ~ l i f f e i , e i i t i germ
~ i t ~ ~cells nit11 lotied nuclei : ~ e
prepoiidcrant (figs. 30 iiiid 32).
33 t o 33 IJiploid 110. 2, 1i* \leeks (control for triploids no. 10 iind no. 11).
Left ovary. Figuics 28. 29 and 33 t o 35 slioir the extremes of \ariation in the
developincnt of o\ arics in controls of this age.
36 t o 38 Tiiploid 110. 11, 18 weeks. Left oviiry. Few oogonia niitl >ouiig oocytes.
Figures 37 aiid 35 rrsenible :in anclifferciitiated goii:rd, except f o r preseiice of a.
ccntral cavity.
245
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