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Studies on sex reversal in Amblystoma. V. The structure of ovaries of a. Tigrinum subjected for long periods to the influence of a testis resident in the same animal

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STUDIES ON SEX REVERSAL I N AMBLYSTOMA
V. T H E STRUCTURE O F OVARIES O F A. TIQRINUM SUBJECTED FOR
LONG PERIODS T O T H E INFLUENCE O F A TESTIS RESIDENT
IN THE SAME
ANIMAL^
R. R. HUMPHREY
Department of A n a t o m y , School of Medicine, University of Buffalo
TWO PLATES (TEN FIGURES)
INTRODUCTION
In an earlier paper of this series ('29) the author described the reduction of the ovary of Amblystoma tigrinum
t o a rudimentary or vestigial state through the influence of a
testis resident in the same animal. A similar modification of
the ovary in this species has since been described by Burns
('30) for females joined in parabiosis to males. In a later
study of this modified or rudimentary ovary the author
found ('31a) that in many cases, in animals three to five
months of age, it became transformed into a testis in some
portion (or portions) of its extent through the development
of testicular lobules; these, it appeared, arose from the proliferation of groups of germ cells which had not become included in the ovarian cortex at morphological differentiation
of the gonad, but had remained at the hilus of the ovary o r
in the adjacent mesovarium. I n other cases, however, it was
found that the ovary did not undergo reversal into a testis
in the manner noted above, but remained in an atrophic o r
rudimentary state. Such gonads, it was found (Humphrey,
'31 b), quickly regenerated into ovaries of normal structure
following the removal (at ages of four to six months) of the
testis which had originally induced their modification.
l T h i s study has been aided by a grant from the Committee for Research in
Problems of Sex of The National Research Council.
135
THE ANATOMICAL RECORD, VOL. 51. NO.
2
136
E. It. HUMPHREY
I t was suggested by the author ('31 b) that the failure of
certain modified ovaries to undergo reversal t o testes was
probably due to the small number of germ cells remaining
in their proximal or hilar regions after morphological differentiation. It was further suggested that in ovaries remaining f o r an indefinite period under the influence of a testis,
these hilar o r medullary germ cells would probably increase
in number, even though slowly, while the oogonia in the covering epithelium (reduced ovarian cortex) would further
decrease in numbers. Such ovaries would thus eventually become transformed into gonads of testicular structure, incapable of regeneration as ovaries even when released from the
influence of the testis originally inducing their atrophy.
The present paper records the results of an attempt to
test by further experiments the suggestions noted above. In
the pages that follow it will be pointed out that the modified
or rudimentary ovary, while in many cases undergoing a
delayed reversal into a testis as anticipated, in other cases
fails t o do so, and may in some instances eventually become
reduced to an essentially sterile structure, probably without
capacity f o r regeneration either as an ovary o r a testis.
PROCEDURE
To secure animals in which the ovary might develop under
the influence of a testis, the gonadic preprimordium was removed from embryos of stages 24 t o 32 (Harrison's series
of standard stages) and replaced by the corresponding preprimordium from a donor embryo of the same stage. The
technique for this operation has been previously reported
(Humphrey, '29). The gonad developing from such orthotopic traiisplants is, in the majority of cases, entirely normal
in its position and relations. The morphological character
of the gonads in any host was determined by exploratory
operation at from f o u r to seven months after transplantation
of the gonadic preprimordium, by similar operation at later
periods, o r by dissection and study after the death or sacrifice of the animal. I t was thus ascertained that in fifty-two
SEX REVERSAL I N AMBLYSTOMA
137
out of 101 grafted animals, the two gonads were unlike in
type, one being a testis, the other an ovary in some stage of
modification or reversal. This number corresponds closely
to the expectation for a species in which the sexes occur in
equal numbers, and indicates the absence of any disturbance
in sex differentiation due to the laboratory environment.
The reversal of any modified ovary into a testis was commonly detected by exploratory operation, the lobes or enlargements consisting of testicular lobules being readily seen with
a binocular microscope. Failure to detect such lobes or enlargements at exploratory operation was never regarded as
sufficient proof of their absence: all such cases were eventually autopsied and their gonads studied carefully under the
binocular microscope after fixation, and, in all doubtful cases,
under higher magnification after being serially sectioned. I n
a few animals on which exploratory operations had shown
the ovary to be reduced to a rudimentary state, the testis
responsible for this condition was removed in order to test
the regenerative capacity of the ovarian cortex. These animals were autopsied at intervals after such unilateral castration and their remaining gonads studied in serial sections.
Bouin’s fixation was used on all material; and serial sections
of the gonads were stained with Mayer’s hematoxylin and
counterstained with eosin.
RESULTS
Of the fifty-two animals in which an ovary was placed
under the influence of a testis, twenty-five were males, the
ovary being that developed from the transplant introduced
in embryonic stages, while the remaining twenty-seven were
females in which that transplant had given rise to a testis.
Since there is no essential difference between the results
obtained in these tu7o groups, they need not be discussed
separately. The ovary, whether that of the host animal or
that derived from the graft, was invariably reduced t o a
rudimentary o r vestigial state under the influence of the
testis developing simultaneously in the same animal. In no
138
R. R. HUMPHREY
instance was it able to effectively inhibit the development of
this testis and induce its reversal into an ovary; in this respect the results of the present experiment agree with those
reported previously (Humphrey, '31 a ) and differ from those
of Burns ( '30), who found that in a small proportion of cases
the testes of A. tigrinum underwent reversal to ovaries in
males joined in parabiosis to females.
Many of the modified or rudimentary ovaries of the present
experiment were found to undergo reversal to testes in the
fashion previously described ( '31 a ) ; f o r details of the morphological features of this reversal the reader is referred to
the paper noted. It is sufficient here to point out that in this
reversal, testicular lobules commonly do not develop throughout the entire extent of the modified 'ovary, but make their
appearance only in a limited portion (or portions) of .its
extent, the gonad thus for a time at least becoming a structure
in which one or more enlargements or lobes of testicular
structure are associated with a variable extent of atrophic
ovary in which no development of testicular lobules has occurred (consult Humphrey, '31 a, figs. 30 to 34). Such lobes
or enlargements of testicular structure were found to have
developed in twenty-two out of fifty-three possible cases in
animals reared in 1929. I n the present experiment (animals
operated upon in 1930) a higher proportion of the modified
ovaries developed a testicular structure (48 per cent as compared with 41.5 per cent in 1929). This difference, it will be
brought out, is due to the greater length of time the animals
of the present series were allowed to live before autopsy or
before removal of the testis which had induced modification
of the ovary.
The development of testicular lobules t o produce an enlargement or lobe in any portion of an atrophic ovary, as
the writer has previously pointed out ('31 a), appears to be
due t o the proliferation of germ cells (potentially spermatogonia) which at morphological differentiation do not become
included in the ovarian cortex, but remain at the hilus of
the ovary or in the adjacenl mesovarium. Tf'these germ cells
SEX REVERSAL IN AMBLYSTOMA
139
are abundant in any particular region, their proliferation will
result in the formation of testicular lobules a t a relatively
early period (animals three to six months of age). I n the
present experiment, it was found that at least seventeen of
the fifty-two atrophic ovaries possessed testicular lobes or
enlargements in some portion of their extent before the animal reached the age of seven months. Eleven of the seventeen animals were autopsied before this age; in the remaining six the presence of a testicular lobe was determined by
a satisfactory exploratory operation. These lobes were variable in their size, in their location in the ovary, and in the
stage of spermatogenesis which they exhibited-these variations corresponding to those previously encountered and described by the writer ( '31 a).
I n those atrophic ovaries in which extracortical (hilar or
medullary) germ cells occur in smaller numbers o r are more
widely scattered in smaller groups along the length of the
organ, it would seem logical to expect that their proliferation
to form testicular lobules might be somewhat delayed, but
that it would nevertheless occur in due time if the gonad
were allowed to remain subject to testicular influence sufficient to prevent its regeneration as an ovary. Among the
fifty-three modified ovaries studied in 1929, a considerable
number were relieved of the inhibitory influence of the testis
through its removal by operation at ages varying from four
to seven months. I n such modified ovaries a regeneration of
the cortex occurred promptly in all cases in which the ovary
had not already become converted into a testis in some portion of its extent (Humphrey, '31 b). I n the present experiment the modified ovary was allowed to continue under the
influence of the testis for longer periods of time. If exploratory operation, at six to seven months after grafting, failed
to reveal a development of testicular lobules in such an ovary,
the testis was not removed, and the animal was kept for subsequent exploration or autopsy, sometimes after the lapse
of several months. I n such cases it was frequently discovered that one or more testicular lobes or enlargements had
140
B. R. HUMPHREY
developed. Two such lobes, whose small size is indicative
of their recent development, are shown widely separated in
the atrophic ovary of figure 1, from an animal autopsied at
approximately eleven months of age. Of twenty-four modified ovaries showing no testicular lobes or enlargements at
exploratory operations between six and seven months of
age, eight, or one-third of the total, exhibited lobes of apparently recent development at exploration or autopsy two to
four months later. I n certain of the other sixteen ovaries,
in which lobes or enlargements had not yet developed, a considerable number of germ cells were nevertheless present,
indicating the probability that a like formation of testicular
lobes would soon have occurred had not the death of the
animal prevented. Such an ovary is shown in figure 2 and in
transection in figure 5. Its cortex contains very few germ
cells ; its proximal o r hilar portion on the other hand, as illustrated in figure 5 , contains a considerable number of spermatogonia. The latter, however, have not proliferated at
any point to form an enlargement or testicular lobe such as
those of figure 1.
I n one animal of the series there was encountered a rather
unusual transformation of the modified ovary which seems
worthy of further comment. The donor furnishing the transplant for this animal was known to be a male, and an exploratory operation 189 days after grafting showed that the ovary
of the host (left) had been reduced t o a vestigial condition
under the influence of the testis derived from the transplant.
No testicular lobules could be observed in any portion of this
ovary. The animal was kept f o r over seven months following
the exploratory operation above mentioned. When finally
killed (412 days after grafting at stage 29) its gonads presented the gross appearance shown in figure 3. The graft
testis (at reader’s left) is of atypical form, due t o adhesions
t o the body wall, and is rather flattened and slender as a
result of the recent emptying or degeneration of many of its
lobules. The gonad of the host (seen at exploratory operation as an atrophic ovary) has become transformed into a
SEX REVERSAL IN AMBLYSTOMA
141
testis by the development of testicular lobules throughout
almost its entire extent (fig. 3, a t right). Since these lobules
are of small size and contaiii no germ cells more advanced
than spermatogonial stages, their recent development is indicated. The unusual feature exhibited by this gonad is the
rather uniform distribution of testicular lobules throughout
a large portion of its extent, as contrasted with the localized
development of lobules commonly encountered (illustrated in
fig. 1and in figures previously published : '31 a, '31 b). aside
from short cephalic and caudal regions which have the form
of a modified ovary reduced to a sterile condition, this gonad
is structurally a testis such as might be found in a male of
three to five months of age. It shows no ovarian cortex in
sections through its enlarged portions and no other structural features to prove its development from a modified ovary.
Naturally, the source of the germ cells responsible f o r the
development of testicular lobules in this gonad is a question
of considerable interest. Two possibilities are presented.
1) Germ cells may have been rather uniformly distributed
along the hilar portion of the modified ovary, but in relatively small numbers (as in the ovary of figs. 2 and 5 ) ; a
uniform increase in such cells would then eventually result
in the formation of testicular lobules more or less simultaneously along the entire length of the organ. 2) The germ cells
may have been derived from the cortex (covering germinal
epithelium) of the ovary as it underwent modification. The
writer is not inclined to regard this as the usual source of
the germ cells responsible for the development of testicular
lobules in modified ovaries ; the evidence, in most cases, indicates rather that such cells are those of the hilar region, and
that the cells of the cortex degenerate rather than migrate
into the interior of the gonad to play a part in its transformation. I n a few specimens encountered in the present
experiment, however, the structure of the gonad suggests
strongly that just such a migration may have occurred. One
such gonad is shown in transection in figure 6. It shows
the division into two parts which is so commonly found in
142
R. R. H U M P H R E Y
atrophic ovaries of A. tigrinum: I.) a promixal o r hilar portion which contains a longitudinal duct (cut in transection) and
a moderate number of germ cells, and, 2) a distal portion which
ordinarily shows few or no germ cells except in its covering
epithelium, which represents the atrophic ovarian cortex. In
this specimen, however, only an occasional germ cell is found
in the epithelium, which has become reduced to a rather flattened type, while the interior, on the other hand, contains
large numbers of cells, chiefly of spermatogonial (oogonial)
type, often arranged in small groups suggestive of early
testicular lobules. A structure comparable to that illustrated
in figure 6 is found throughout a large part of the length of
this atrophic ovary, which has at its caudal end a lobe or
enlargement, comparable to one of those of figure 1, containing numerous testicular lobules. It is entirely probable that
the portion of the gonad represented by figure 6 would
shortly have given rise to testicular lobules and thus have
attained a structure comparable to that of the transformed
gonad of figure 3.
Whether or not oogonilz have actually migrated into the
interior of the gonads above described cannot be positively
decided. Such a migration, however, should it occur, would
doubtless tend to take place rather uniformly along a large
extent of the modified ovary, and would hence tend to bring
about the rather uniform transformation of the gonad into a
testis, rather than the transformation of limited regions only,
as occurs in the vast majority of cases (fig. I).
While the possibility of a migration of oogonia into the
interior cannot be denied, and while it is even strongly suggested in occasional instances such as the cases discussed
above, there are nevertheless many cases in which it must
fail to occur-cases in which the modified ovary remains as a
vestigial structure for a year or more, no testicular lobules
developing in any portion of its extent. Ten animals of the
present series were found to have no testicular lobes or enlargements when killed at ages of ten to fourteen months.
In only one of these animals did the atrophic ovary show a
SEX REVERSAL I N AMBLYSTOMA
143
structure at all comparable to that illustrated in figure 6; in
the others the distal portion of the gonad contained few or
no germ cells, except those oogonia persisting in its covering
epithelium. I n figure 4 is shown the gross appearance of the
graft ovary in a male host killed 411 days after transplantation of the gonadic preprimordium. This ovary appears as a
very thin, flattened membranous fold. Its appearance in sections is shown in figure 7. Altogether only two or three
dozen oogonia remain in its epithelium, scattered singly along
its free margin, while only three o r four germ cells are found
in its hilus. I n several other animals of this group (age, ten
to thirteen months at autopsy) the germ cells of the cortex
are only slightly more numerous, while those of the hilus are
few or even entirely lacking. I n one atrophic ovary (fig. 8)
only seven germ cells in all could be identified; of these, six
were in the interior and one in the epithelium. The structure
of ovaries such as these quite clearly indicates a progressive
degeneration and disappearance of the oogonia of the cortex
rather than their migration into the interior. Those few
germ cells found in the interior at autopsy are doubtless in
most cases cells which remained in that situation at the time
morphological differentiation of the gonad occurred ; only
occasionally are such cells evztirely absent from the hilar
region of the normal ovary. Their failure to multiply in the
modified ovary is probably to be charged to their isolation
and to the absence of an adequate endocrine stimulus. Accompanying the atrophy of the ovary in any host there occurs
an hypertrophy of the testis which had caused its modification; such testes have been found to average far higher in
weight than the testes of normal males. This hypertrophy
possibly serves to prevent the adequate stimulus of the
atrophic ovary by anterior-lobe hormones, and hence postpones o r prevents its reversal into a testis.
The regenerative capacity of the ovarian cortex after longcontinued degeneration of its germ cells should, naturally,
become greatly reduced. I n a previous series of experiments
('31 b) it was found that any modified ovary quickly regen-
144
R. R. HUMPHREY
erated t o a normal structure when the testis which had caused
its atrophy was removed before the animal had reached the
age of five months. The modified ovaries of animals of this
age were found, on sectioning, to have large numbers of germ
cells remaining in their covering epithelium ; these furnish
the basis for a prompt regeneration of the normal ovarian
cortex. In the present experiment, in order to further reduce
the number of such cortical germ cells, the testis was not
removed until the animal was approximately nine months of
age. Of ten such unilaterally castrated animals, four were
found a t autopsy to have developed testicular lobes or enlargements in some portion of the atrophic ovary, either preceding or coincident with castration ; these we may disregard,
since the presence of such a testicular structure has been
found sufficient of itself either t o retard or to completely
inhibit the regeneration of the ovarian cortex (Humphrey,
'31 b). I n the remaining six animals the atrophic ovaries
showed no testicular lobules in any part of their extent.
Of the six, only one, killed thirty-six days after unilateral
castration, shows any marked regeneration of the cortex in
the atrophic ovary. I n this gonad (fig. 9) considerable
numbers of oocytes are found, many of them already beginning enlargement. In another animal, killed sixty days after
castration, the ovary has a considerable number of oogonia
in its epithelium, and there is evidence that these are increasing by mitosis (fig. 10) ; regeneration here must be regarded
as being greatly retarded, probably due to the very small
number of germ cells remaining in the ovary at castration.
I n two other animals killed at three weeks, the structure
of the atrophic ovary is similar to that of figure 10, and
may be interpreted as indicating an early stage of cortical
regeneration. I n the two remaining animals the ovary contains so few germ cells as t o be, in a large part of its extent,
completely sterile. A typical section of one of these ovaries
is shown in figure 8; this gonad contains altogether only
seven germ cells, only oqze of which is in its covering epithelium. The regeneration of a normal ovarian cortex in such
SEX REVERSAL I N AMBLYSTOMA
145
a gonad is naturally an impossibility, unless the indifferent
cells of the epithelium are able to transform into germ cells.
This they seem not t o have done in this ovary, although the
testis responsible for its atrophic state had been removed
forty-five days previous to autopsy and the animal was apparently in good health during this interval. I n another
animal, castrated for thirty-six days, the atrophic ovary is
similar to that shown in figure 8, but contains a slightly
larger number of germ cells.
DISCUSSION
I n previous experiments reported by the writer ( ’31a and
b) and by Burns ( ’30) ovaries of A. tigrinum were kept under
the influence of a testis for much shorter periods than in the
present study. I n no instance was the influence of the testis
(or male parabiotic twin) maintained for a period longer
than six months. The structure of the modified ovaries at
this time and at earlier periods, in Burns’ material, leads him
(’30) to state that they “attain virtual transformation into
rudimentary testes which are believed capable of regeneration into a functional organ.” The writer (’31a ) first described the actual transformation of many such rudimentary
gonads into functional testes, but found that those rudimentary gonads in which testicular lobules had not developed
commonly underwent regeneration into ovaries if the testes
which had induced their modification were removed by operation before the hosts reached the age of six months ( ’31 b).
This suggested the present experiment, designed to test the
persistence of regenerative capacity in the ovarian cortex and
to determine whether all modified ovaries might not undergo
reversal, providing their cortical regeneration were inhibited
for an indefinite period.
The results obtained in the present experiment show that
while many ovaries undergo reversal within three to six
months, the development of testicular lobules in others is
either greatly delayed or even fails t o occur after the ovary
has remained under the influence of a testis for a year or
146
R. R. HUMPHREY
more. Similarly, ovaries relieved of the influence of a testis
at the eighth month or later differ greatly in their capacity
for regeneration. These differences in capacity of the modified ovary for regeneration or for reversal appear to depend
upon, 1)the rate at which the ovarian cortex atrophies under
the inhibitory influence of the testis, and, 2) the mode of distribution of the germ cells at the time of morphological differentiation of the gonad, and the rate of increase of those
cells which do not become included in the cortex.
The number of oogonia in the cortex of the modified ovary
appears t o undergo a progressive decrease when the inhibitory action of the testis is continued indefinitely. With this
decrease is correlated the diminished regenerative capacity
of the cortex following removal of the testis which had
caused its atrophy. I n not all cases, however, do the numbers
of oogonia decrease at the same rate. Some ovaries, after
ten months' development under the influence of a testis, may
still have a considerable number of oogonia in their covering
epithelium, while others have very few o r practically none
at all. Those gonads with many oogonia persisting may regenerate into normal ovaries following removal of the
inhibitory action of the testis. On the other hand, in those
extreme cases in which few or no germ cells rcmain in the
cortex, the regeneration of the gonad as an ovary either fails
to occur or is very greatly delayed, as in certain ovaries of
the present experiment.
The number of germ cells remaining outside the cortex in
a hilar or medullary position at the time of morphological
differentiation of the gonad is likewise highly variable (Humphrey, '31 a ) . If the number of such cells in any modified
ovary is large, their proliferation may result in the formation
of testicular lobules at an early period; the modified ovary
may thus attain the structure of a functional testis in a part
of its extent even in a host six months of age or younger.
I n other cases in which the extracortical germ cells are fewer,
or in which their proliferation occurs less rapidly, the formation of testicular lobules may be delayed for a variable period.
SEX REVERSAL I N AMBLYSTOMA
147
I n still other ovaries in which the germ cells of the hilus or
medulla are very few in number (or are entirely lacking?)
no development of testicular lobules occurs even after a year
or more.
Although the migration of oogonia into the interior of the
modified ovary is possible and is indicated as occurring in
some few cases, it nevertheless must fail to take place in
numerous other ovaries, in which the cells of the interior
still remain few in number even after oogonia have practically disappeared from the covering epithelium. This is in
contrast with the condition described by Witschi (’29) in
ovaries of Rana sylvatica tadpoles undergoing reversal to
testes following the application of high temperature. A
transformation of duct cells into spermatogonia, as described
by Hargitt ( ’24) for Diemyctylus (Triturus) likewise seems
not to occur in such modified ovaries. Receiving few or no
germ cells at morphological differentiation, and acquiring
none at later periods by migration from the ovarian cortex
or by transformation of duct cells, the hilar or medullary
portions of these ovaries fail t o develop a testicular structure,
but remain in an essentially sterile condition. An ovary of
this type, after the final disappearance of the oogonia of its
cortex, would probably have little or no capacity for regeneration into either an ovary or a testis, even when relieved
of the inhibitory action of the normal testis. To such an
ovary, sterile o r essentially so, the term ‘freemartin gonad’
would seem entirely applicable.
SUMMARY AND CONCLUSIONS
1. Ovaries of Amblystoma tigrinum kept continuously
under the influence of a testis from embryonic life onward
may either undergo reversal to testes or remain in a rudimentary or vestigial state.
2. The time at which reversal of the modified ovary occurs
(i.e., the time at which testicular lobules develop) is variable.
It appears to depend upon the number and arrangement of
the germ cells which remain in a hilar or medullary position
148
R. B. HUMPHREY
at morphological differentiation of the gonad, and upon the
rate at which these cells proliferate.
3. Ovaries which remain indefinitely in a rudimentary or
vestigial condition possess few or no germ cells in their hilar
or medullary position; the absence of such germ cells (or thc
failure of isolated cells to proliferate) precludes the development of testicular lobules essential t o complete reversal.
4.The germ cells of the ovarian cortex decrease in numbers
as the influence of the testis is continued. Since in one case
only a single cell remained, it is concluded that the germ cells
of the cortex may ultimately disappear completely.
5. The regenerative capacity of the ovarian cortex decreases as its germ cells become reduced in number. Ovaries
relieved of the influence of a testis after their cortical germ
cells have become greatly reduced in numbers regenerate
slowly, if at all.
L I T E R A T U R E CITED
BURNS,R. K., JR. 1930 The process of sex transformation in parabiotic Amblystoma. I. Transformatioil f r o m female to male. Jour. Exp. Zool.,
VOI. 55, pp. 123-169.
HARGITT,G. T. 1924 Germ-cell origin in the adult salamander, Diemyctylus
viridesceiis. Jour. Morph. a n d Phpsiol., vol. 39, pp. 63-111.
HUMPHREY,
R. R. 1929 Studies 011 sex reversal i n Amblystoma. 11. Sex differciitiatioii and modification f ollowiiig orthotopic implaiitatioii of a
goiiadic preprimordium. Jour. Exp. Zool., vol. 53, pp. 171-220.
1930 a Studies on sex reversal in Amblystoma. 111. Transformation of the ovary of A. tigriiium into a functional testis through the
iiiflueiice of a testis resident in the same animal. Jour. Exp. Zool.,
V O ~ . 58, pp. 333-366.
____1930 b Studies 011 sex reversal in Amblystoma. JV. The developmeiital poteiicies exhibited by the modified ( ‘freemartin’) ovary of
.4. tigriiium followiiig removal of the testis which had induced its
modification. Jour. Exp. Zool., vol. 58, pp. 367-400.
WITSCHI,E. 1929 Studies on sex differeiitiatioii and sex determiiiatioii in
amphibians. 11. Sex reversal in female tadpoles of Raiia sylvatica
following the application of high temperature. Jour. Exp. Zool.,
VOI. 52, 11p. 267-292.
PLATES
149
PLATE 1
EXPLANATION OF FIGURES
All figures on this plate are photographs ( X 4 ) of dissections of host animals.
The gonads remain in situ, exposed by removal of the gastro-intestinal tract
and the f a t bodies. In each figure the gonad derived from the engrafted gonadic
preprimordium (right) is seen at the reader’s left.
1 Female host no. 266, killed 324 days a f t e r implaiitatioii at stage 30 of a
goiiadic preprimordium from a male donor. Note the large testis derived from
the graft. The slender modificd ovary of the host shows two testicular lobes
or enlargements (see arrows) whose recent development is indicated by the small
size of their eompoiient lobules.
2 Female host no. 47, 405 days a f t e r implaiitatioii at stage 29 of a gonadic
preprimordium from a male donor. Note the large testis derived from the graft.
The modified ovary of the host (see arrow) shows no enlargements comparable
to those of figure 1, but on sectioning is found to have considerable numbers of
germ cells in its hilar portion (fig. 5 ) .
3 Female host no. 237, killed 412 days a f t e r implaiitation at stage 29 of a
goiiadic preprimordium from a male donor. The testis derived from the g r a f t
(at reader’s l e f t ) is of atypical form due to adhesions, and is of small size due
to the reccnt emptying of its lobules. The ovary of the host (at right), found
by exploratory operation seven months previously to be reduced to a vestigial
state, has now become transformed into a testis throughout almost its entire
extent.
4 Male host no. 271, killed 411 days after implantation at stage 30 of a
goiiadic preprimordium from a female donor. Thc ovary derived from the g r a f t
(sec arrow) has been reduced to a thin, membranous fold i n which but very
few germ cells remain. I t s appearance in sections is shown i n figure 7.
150
SEX REVERSAL I N AhlELYSTOMA
PLATE 1
R . R. HUXPHREY
151
PLATE 2
EXPLANATION
O F FIGURES
All figures on this plate are 1~liotomicrogiaphsof trailseetioils of ovariea
rctluccd to a rudimeiitaiy or vestigial state under the influeiire of a testis. X 150.
5 Ovary of female host 110. 47, 405 days a f t e r implantation a t stage 29 of a
goiiadic preprimordium from a male donor (for gross appearance of gonads, seo
fig. 2 j . This ovary has very few germ cells remaining ill its coveriiig epithelium
(none in this seetioil), b u t has a eoiisidcrable number of spermatogonia iii its
proximal or hilar portion.
6 Ovary of female host 110. 228, killed 326 days a f t e r implalitstion at
stage 29 of a gonadic: l ~ r q r i i n o r d i u mfroin a male donor. This ovary has very
few germ cells remaining in its covering epithelium ( o w appears a t lowcr edge
of figure), hut coiitains largc number3 of ~ u c l icells ill the iiitrrior of its distal
portion, a region in which few or 1 1 0 1 1 ~ are ordiiiarily fouiid. Compare figure 5 ;
ser also page 141.
7 Graft ovary of male host 110. 271, killrd 411 days a f t e r implantation at
stage 30 of a goiiadic preprimordiuin frorri a female donor. This ovary eoutaiils
a very small iiumber of gerin cells, almost all of which are found siiigly iii the
covering epithelium of its free margin, as in this figure (see arrow). F o r gross
appearance see figure 4.
8 Ovary of female host no. 61, killed 314 days after implantation at stage 30
of a goiiadic preprimordium from a male donor. This ovary coiitaiiis oiily seven
germ cells (iione showii in this section), six of which lie in its interior. It
shows iio regelleratioil of the ovarian cortrx, although the g r a f t testis had been
removed by operation forty-five days previous t o autopsy.
9 Graft ovary from male host 110. 232, killed 302 days a f t e r implantation
of the goiiadic Ineprimorclium and thirty-six days a f t e r removal of the tcstis
of the host. This ovary shows a pronounced regelleratioil of the cortex in many
regions ; iiote the enlarged ooeytes iii this scction. The ovarian cavity, howccer,
is still lacking.
10 Graft ovary from male host 110. 58, killed 329 days a f t e r implaiitation of
the goiiadie preprimordium and sixty days after removal of the testis of the host.
This ovary is less advaiiced in regeneratioil than that showii i n figure 9. Germ
cells are fairly iiumerous in its cortex, however, and are occasionally secii in
mitosis; this figure shows one in a prophase stage (see arrow).
152
SEX REVERSAL I N A3lBLYSTOMA
PLATE 2
R. R. HUMPHREY
153
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amblystoma, reversal, long, testis, resident, tigrinus, subjected, influence, ovaries, sex, structure, period, animals, studies
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