STUDIES ON SEX DIFFERENTIATION
IN FOWLS.
BY G. F. FINLAY.
{From the School of Agriculture, Cambridge, and the Animal
Breeding Research Department, Edinburgh)
W I T H SIX PLATES.
(: O N T E N T S
PAOI
I. Introduction
.
.
.
.
2. Preliminary Experiments .
(a) Physiological Factors affecting Hen-feathering .
(6) Gonad Transplantation in
Growing Chicks
3. Castration and Gonad Transplantation in Newly Hatched
Chicks
General Method—Technique—
Castration of Males—Ovariotomy of Females—Grafting—
After treatment
>
Classification of the Experimental G r o u p s . . . .
I.
PAOl
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Males with Testis
Males without Gonads
Males with Ovary
Males with both Testis a n d
Ovary
Females with Testis .
Females without Gonads .
Females with Ovaries
Females with both Testis a n d
Ovary
Comparison of the E i g h t Experimental Groups
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.
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4. Discussion
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5. Conclusions
6. References
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Introduction.
FOR this investigation the fowl was chosen because of its
marked sex dimorphism and its ability to withstand operative
interference. The work was commenced and carried to an
advanced stage at the School of Agriculture at Cambridge;
later the birds were transferred to the Animal Breeding Research
Department, Edinburgh. I wish to thank Dr F. H. A.
Marshall, Dr F. A. E. Crew, Professor R. C. Punnett, and
Mr S. T. P. Strangeways, for helping me in various ways
during the course of the experiments. The histological part
of this study has been carried out by Mr A. W. Greenwood
and is reported in a separate paper.
The funds for this work were provided largely from grants
from the Ministry of Agriculture administered through the
Animal Nutrition Institute, Cambridge. The writer also
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G. F. Finlay
received grants as a holder of the Walter and Eliza Hall
Veterinary Research Fellowship of Sydney University.
2. Preliminary Experiments.
(a) Physiological Factors affecting: Hen-feathering.—Morgan
has suggested that in the male Sebright, which has feathers
of the henny type, the inhibitor of cocky feathering is located
in the luteal cells of the testis of this breed. The logical
conclusion, if one were to accept this hypothesis, would be
that there must be more than one male sex-hormone, or that
this internal secretion of the testis is not of a fixed character.
In order to test this point attempts were made to graft
testis from males of the hen-feathered variety into males with
the more common cocky plumage to see if the cocky plumage
of the latter would be inhibited. Attempts were also made
to graft testis from the cocky feathered birds into the castrated
henny feathered males. Unfortunately the grafts did not take.
This may have been due to the fact that the birds were fully
grown with the testis in a state of active spermatogenesis,
and hence unsuitable for grafting; or possibly to the fact
that the birds were of rather heterozygous constitution. This
experiment is only mentioned here to show that it formed one
of the series, and also because it indicates what are unfavourable
conditions under which to attempt gonad transplantation.
Castration of Guinea-Fowls.—The guinea-fowl has feathers
of the henny type in both sexes. Two male birds were castrated
when just under 6 months old to see if these birds would
develop feathers of the common cocky type, when the influence
of the testis was removed. At the time of the operation the
testes were about the size and shape of haricot beans and were
removed without difficulty. On post-mortem examination the
castration was shown to have been complete. The birds
remained in good health and feather until they were killed about
fourteen months later. During this period moulting seemed
to be going on fairly continuously, for loose feathers were
always to be seen lying about, and no radical moult, as in the
other fowls, took place. No change in the character of the
new feathers was apparent. This experiment, therefore, indicates
that the henny feathering of the male guinea-fowls is funda440
Studies on Sex Differentiation in Fowls
mentally different from that of the Sebright bantam and other
hen-feathered varieties of the domestic fowl.
(6) Gonad Transplantation in Growing Chicks—A Feminised
Male Fowl.—Previous workers in this field have usually operated
upon chicks during the actively growing period, hence it has
been somewhat difficult to know just what the influence of
the gonads on sexual differentiation during the early period
of development has been.
One of my earlier cases is worth describing because it has
some bearing upon the theory of gonad differentiation. This
bird was a male chick, exact age unknown, but was about
6 weeks to 2 months old. The sex was fairly evident at
this stage. It was castrated on both sides, and the chopped
ovary from a young female inserted into the abdominal cavity.
This bird (fig. 1, Plate VI.) showed the influence of the graft
plainly. As regards feathering it was henny except for slight
sickles in the tail. Its comb was very like that of a hen. The
spurs were typically masculine. In behaviour it had some of
the characteristics of a hen, though it was reported to me
that it was seen occasionally to tread other hens. It never
crowed, but was in the habit of singing. It did not behave
like an asexed type, though it was difficult to say that it
was definitely feminine. It would be more correct to describe
it as abnormally sexed.
It was killed when 11 months old. There was no trace of
testis, but a flat ovary about 1 inch by \ inch was growing
in the mesentery. This case indicated that the ovary stimulated comb growth, but not to the same extent as the testis
would have done if it had been left to function. The ovary
(fig. 2, Plate VI.) is apparently normal, and this point is of
some interest in the light of the ovarian transplantations
which are described later.
The castration and other experiments performed on other
types at this stage are not described, because they did not give
any important information on the questions involved.
I came to the conclusion that much better tests could be
made if the operations were done on chicks just after hatching,
in order to control the interaction between gonad and soma
during practically the whole of the growing period. In general
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G. F. Finlay
the first third of the growing period had been neglected by
previous operators. As a preliminary experiment ten chicks
about 4 days old were operated on in various ways—chiefly
castrations and transplantations of gonads. All of the ten
chicks survived till maturity, and though the operations were
mostly failures, they indicated the possibilities of a valuable
technique. The failures consisted mainly in the regeneration
of small pieces of testes left behind, which grew into nearly full
sized testes. Several, however, were completely castrated on
one side. One case merits further description.
A Case of Experimental Hermaphroditism in a Pullet.—
A Columbian Wyandotte female chick was operated on when
4 days old. It was anaesthetised and its body opened through
the last intercostal space of the left side, and four testes from
two chicks of the same age were inserted through the intercostal
opening. When about 5 months old it was noted that this
bird had the typical body and plumage of a pullet, but that it
possessed a coarse masculine comb. The numerous cockerels
about the place paid little or no attention to this bird, while
they favoured other pullets. When about 7 months old it had
every appearance of being in laying condition. It died when
8 months old, due to the stoppage of the oviduct with an
abnormally large egg. There were also several yolks higher up
the oviduct.
Examination revealed that in addition to the normal ovary
a nodule of testis about 1.5 mm. in diameter was projecting
into the abdominal cavity from the site of the operative wound.
This was found to be swarming with actively motile sperm, and
on section showed normal testis tissue.
3- Castration and Gonad Transplantation in Newly Hatched
Chicks.
The partial success achieved with the young chicks in the
foregoing series led me to conclude that it would be profitable
to continue this plan of experiment under more critical conditions. In particular it seemed desirable to use pure-bred
Brown Leghorns, which, because of their relative homozygosity,
would give more accurate comparative results and also because
this breed probably shows more marked sexual differentiation
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than any other breed in this country. Pure-bred typical Brown
Leghorn pullets were mated with an exhibition type cockerel.
Pullets were used in order to obtain a maximum number of
eggs from each female within a limited time. This made it
possible to hatch out fairly large families of full brothers and
sisters. It was perhaps a mistake to use pullets, for chicks
from pullets are generally considered by poultrymen to be rather
weakly. Certainly many of the chicks hatched were cripples
and could not be used. Trapnest records were kept so that the
relationship of the offspring could be determined. There are
indications that grafting operations are more successful when
done between closely related individuals, so it was planned to
graft between brother and sister as far as possible. Chicks
from a second pen, in which a Brown Leghorn cockerel was
mated to Silver Duckwing Leghorn pullets, were also used in
a few cases.
Chicks were successfully operated on as early as 2 days
old. The age recorded in all cases has been reckoned from the
twenty-first day of incubation. These chicks hatched either at
the twentieth or the twenty-first day, and for the operation it
was found to be more convenient to wait until they were 3
days old. During the first two days the yolk sac is large and
easily ruptured. By the third day also the chicks are active,
strong, and accustomed to the brooder.
The incubation was so arranged that groups of full brothers
and sisters would all hatch on a certain day. These would be
all taken to the operating room together and the transplantation
experiments performed as rapidly as possible, so as to prevent
undue exposure of the gonads.
All possible combinations of gonad with soma were made.
The operations were performed without assistance, for it proved
a simple though delicate and tedious procedure. The difficulty
of anaesthetising as reported by Goodale and others was not
experienced, though it was found advisable to have the subject
thoroughly under before opening the abdominal cavity, as the
inhaled ether and air escapes through the wound.
General Method—Technique.—The only instruments used
were a very fine pointed pair of scissors, the smallest silver
probe, a special pair of dissecting forceps with very fine ends
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G. F. Finlay
turned almost at right angles, and suturing material. The
most important item was the light; direct sunlight was found
to be best, while artificial light was quite useless.
The chick was placed in a block of wood about 6 inches by
3 inches by i inch which was hollowed out in the shape of the
chick's body, with grooves for the head, neck, and legs. The
wing was pinned above the body and the down plucked from
the costal region. Sterile instruments were used, but rigid
antiseptic measures were not taken, the skin being merely
damped with warm water for the purpose of pushing aside the
remaining down. The abdominal cavity was opened with
the scissors through the last intercostal space, the air sac was
cut through, and the gonad exposed.
In order to make provision for gonads which might be
removed from a chick's body, several watch-glasses containing
Ringer's solution were placed in covered Petrie dishes which contained a little water, and the whole kept warm in an incubator.
Castration of Males.—The removal of the testis had to be
done very slowly and carefully. If the forceps were placed
above the testis and pulled, the organ would come away, but
a tiny fragment would be left, while the site would be obscured
by haemorrhage. It was found best to start at one end, and
gently free the testis from its attachment bit by bit. To
remove the opposite testis, the chick had to be turned over
and a similar operation performed from the opposite side. The
wounds were closed with two or three of the finest silk sutures.
Ovariotomy of Females.—The removal of the ovary when
the chick is but 2 or 3 days old is a matter of considerable
difficulty. The area of attachment of the ovary had to be
carefully crushed with the fine forceps, and after waiting some
time to allow coagulation, the ovarian tissue was carefully
picked off. By working in direct sunlight one could see when all
the ovarian tissue was removed. As the sex of the chick was
not known until its body cavity was opened, it was first put in
the block with the left side uppermost, then if it proved a female,
the chick was already on the side convenient for ovariotomy.
Grafting.—Any gonad tissue which was removed was
placed in the warm Ringer's solution. When it was desired
to graft a gonad into the chick's body, the site just anterior to
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Studies on Sex Differentiation in Fowls
the kidney was used. This is vascular, and there are strands
of connective tissue there to help immobilise the graft. Another
advantage is that the growing gonad can project into the
abdominal cavity and take up a position quite close to the
normal gonad site. The anterior extremity of the kidney-is in
close proximity to the upper part of the last intercostal space.
After Treatment.—The chicks were placed close to the
fire immediately after operation to recover from the exposure.
A few hours later they seemed to show little or no ill effects
from the operation. Subcutaneous emphysema, however,
invariably followed, the chick sometimes attaining almost
twice its normal size. This, however, did not seem to cause
any inconvenience, for such chicks were quite active and
healthy.
The skin invariably healed by first intention.
Chicks which survived the operation, that is those which
were not killed through haemorrhage during the operation,
almost invariably survived till maturity.
Classification of the Experimental Groups.—As it was desired
to study the reactions of soma and gonad, in all eight
experimental groups were formed. These were as follows :—
Male Groups.—(i) Testes left; (2) castrated; (3) castrated
and ovary engrafted ; (4) testes left and ovary engrafted.
Female Groups.—(1) Ovariotomised and testis engrafted ;
(2) ovariotomised; (3) ovary left; (4) ovary left and testis
engrafted.
During the growing period it seemed as if the experimental
birds were conforming to these groups, and a specimen of each
group was selected and its portrait painted. There were, however, some interesting exceptional cases which will be described
in detail later. Though not strictly accurate the coloured plates
show the eight typical classes. The birds with silver hackles
and saddles are from the second pen in which a Brown Leghorn
was mated with Silver Duckwing Leghorns. However, except
for this silver coloration, these birds are of the same type and
size as those from the first pen.
Bird No. 4 (Plate I.) is the only one which is not a good
specimen of its class. The fact that this bird is only partially
henny in its plumage was thought to be due to the presence
of but a small quantity of engrafted ovary. On post-mortem
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G. F. Finlay
examination this was found to be the case. Other cases
support the view that if a certain amount of ovarian tissue
is present, even in the presence of testis, a nearer approach to
complete hen-feathering will result.
Male Groups.
i. Males with Testio.—Some normal males were reared as controls. In
addition in two cases the vas deferens was resected, and in one case castration
was performed and testis grafted subcutaneously. In all these cases normal
development of the male characters followed.
No. i (Plate I.) can be regarded as a typical Brown Leghorn cock. It was
operated on when a few days old and it was noted that it was a male. Its testes
were left intact and it was stitched up and left as a control. The size of this
bird in relation to that of the representatives of the other seven classes can be
seen by reference to the coloured plates, for in all illustrations care was taken
to depict the birds in their relative sizes. Attention is drawn to the general
body shape—especially the constricted pelvis, the stance, strong but blunt spurs,
large upright comb, large wattles and ear lobes, and the compact black and gold
male plumage.
No. 9 (Plate III.) was castrated when u days old and three testes from
half-brothers grafted subcutaneously on the left side and two testes, also from
half-brothers, on the right side. This bird developed as a normal cock. The
nodules of testes could be felt on the left side. When a year old it was killed
and examined. Subcutaneously, on the left side, there was a testis nodule about
one quarter the size of a normal testis, and also a smaller nodule about the
size of a pea. Motile sperm were observable in the larger graft There was
no trace of any testicular tissue inside the body cavity. The vasa deferentia
were well developed, but were of course empty. I judged from this case in
comparison with many others that the subcutaneous position is not so favourable
for testis growth as inside the body cavity. Vascularisation is not so easily
established, and the graft is constantly subject to slight injury. However, as
regards sperm atogenesis, these subcutaneous grafts were similar to the others.
No. 10 (Plate III.) when n days old was opened and the left vas deferens,
close to its junction with the testis, seized with the forceps and ruptured.
This bird was typically cocky, but was slightly smaller than most of the males.
It was examined when a year old. The right testis was of course normal; the
left also appeared quite normal, and though it was only about three-quarters the
size of the right, this is quite within the normal limits of variation. .The right
vas was full of milky seminal fluid. The left was not connected to the
epididymis, and though otherwise well developed it appeared very different to
the right vas owing to the absence of seminal fluid. From this and other cases
it would appear that a testis can function normally—at least for some months—
without a duct. The sperm collect in a compact mass in the lower end of the
tubules, while the more fluid secretion is evidently reabsorbed.
No. 11 (Plate III.) is given merely as illustration of another normal control cock.
It was not operated on at alL It has the same characteristics as the foregoing birds.
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Studies on Sex Differentiation in Fowls
Review of Group.—It is apparent that testis can grow,
function, and produce full masculinity whether it be in the body
cavity or placed subcutaneously. The latter position, however,
does not appear to be as favourable for growth of this organ
as the body cavity. Case No. 9 (Plate III.) suggests that
about one-seventh of the normal amount of testicular tissue is
sufficient for full development of the sexual characters.
2. Males without Gonoda.—In this group I attempted to perform complete
castration in every case. However, this is very difficult in young chicks, and
one must expect that in some cases a fragment of testicular tissue will be left
Such cases, however, give valuable indications as to the amount of testis
required for full .masculine development; and, I think, show that the reaction
between soma and gonad is a quantitative one.
No. a (Plate I.) was completely castrated when 7 days old. In size it was
much the same as the normal males, and, contrary to what one might expect,
the skeleton was similar. The spurs, however, differed somewhat, in that they
were longer and sharper. It is possible that this was partly due to the inactivity
of the bird, for in normal males the spurs are worn blunt by fighting and scratching. The plumage was of the same general type as the foregoing, but the feathers
were considerably longer and not so compact This was particularly noticeable
in the hackles, saddles, and tail feathers. The comb and wattles remained
infantile. The stance was somewhat different, this bird not having the upright
proud carriage. This perhaps is due to the fact that the capon has not the same
weight of head furnishings and can therefore adopt a more horizontal posture
without changing the centre of gravity; and to the fact that he has not the sex
pride which impels the normal male to assume an upright commanding position.
No. 12 (Plate III.) was operated on when 3 days old. Complete castration
was attempted, but examination when 18 months old showed that a piece of
testis a little over 1 cm. in diameter and weighing a. 7 gm. was present. The
spurs were sharp like those of a typical capon. The comb and wattles were
cocky but were somewhat smaller than those of the normal cocks. The
plumage was very similar to that of a typical capon, though it may have been
somewhat more compact. As regards behaviour, this bird crowed and would
tread hens, but the fact that its spurs were not worn, and that it did not fight
or exhibit marked sexual instincts, showed that it was incompletely sexed.
No. 13 (Plate III.) was also castrated when 3 days old, but a small piece
of testis, about half the size of the piece in No. 12, was found when it was
killed 18 months later. The comb and wattles were considerably smaller'than
in the foregoing, but this bird also would crow and tread hens, though its
sexual instincts were still more suppressed (Plate III.).
No. 14 (Plate III.) is another example of a complete capon, the castration
having been performed when the bird was 4 days old.
Review of Group.—The photographs of Nos. 12, 13, and
14. were taken when these birds were 50 to 51 weeks old;
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G. F. Finlay
and as they were all in good condition, the photographs give a
very good indication of the quantitative relation between
amount of testis and comb size. Previous experience had led
me to always expect that when less than one-eighth of the
normal amount of testis tissue was present, there was a degree
of development of the head furnishings in quantitative relation
to the size of the testis nodule left. More than that amount
caused normal masculine development. A comparison of the
measurements of the head furnishings of these fowls is given
in the table of measurements. As regards behaviour, these
cases indicated that manifestations of masculinity also varied
according to the amount of testis present.
3. Males with Ovary—With this group of birds complete castration was
attempted, and at the same time some ovarian tissue was engrafted. This
proved to be a particularly interesting group, because the ovary grafts either
developed as ovarian tissue or became transformed into testicular tissue.
Furthermore the time relationship gave some indication of the period in development when the ovary could be changed by environment. The group also indicates
to some extent the degree to which feminisation of the male can be effected.
No. 3 (Plate I.), when nearly 11 months old, and in Plate IV. when 7
months old. It was castrated when 6 days old, and two ovaries from sisters
engrafted, one being put in each side. This bird was of the same size as the
other males, and it possessed spurs like those of normal cocks. Its skeleton
was like that of a cock, the pelvis being of the constricted male type. However,
the secondary sexual characters were henny. The plumage was of the colour
of a hen, the breast being salmon instead of black, while the rest of the plumage
was the sombre brown of the hen. The back feathers, however, showed slight
masculine tips, while the tail was larger than in normal hens. As can be seen
from the photograph at 7 months the head furnishings are very much the same
as those of pullets of that age.
As regards behaviour and mentality, it was difficult to draw exact conclusions.
This bird had not that lack of pride which characterises asexed birds. On the
other hand it did not make any sexual advances towards other fowls, nor did
it receive them. I suggest that it would be fairly accurate to describe it as
having the general mental characteristics of the male without the aggressiveness
and desire to lead which develops with the male secondary sexual characters.
But this and similar birds had not the timid, shy disposition of pullets. When
attacked it would repel its opponent vigorously and without fuss. These birds
were the most peaceful in the pens, but they would resist attack.
When killed just after the painting was made, examination revealed a normal
ovary on the left side, just anterior to the kidney. It appeared to be about
half the usual size, and there were yolks in all stages of development, the
largest being almost ready to escape. The germinal spot was present. Some
yolks had evidently already escaped, judging from the presence of free fluid
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Studies on Sex Differentiation in Fowls
yolk in the abdominal cavity. On the right side was a small undeveloped
ovary.
On the left side, attached to the last intercostal muscles, was a testis nodule
about 1.5 cm. in diameter. It may be assumed that this nodule had the effect
of causing a slight tipping of the feathers, and of stimulating comb growth to
a slight extent. It is interesting to note, however, that this testis nodule did
not cause masculine comb development up to 7 months of age, as can be
seen from the photograph on Plate IV., nor did it evoke the sexual desires of
the cock.
No. 15 (Plate III.) was castrated when a days old and an ovary from a sister
was engrafted into each side. This bird grew up as a vigorous cock. The
hackles were rather shorter than in a typical cock; the back feathers and
saddles intermediate; while the comb and wattles were fully masculine. In
behaviour this bird was fully cocky; it crowed often and would tread hens
normally.
Post-mortem examination, when a year old, showed a small nodule of testis
the sire of a pea on the left testicular site. This was quite insufficient to cause
masculine secondary sexual characters to develop to any noticeable degree;
and if this had been the only gonad tissue present, the bird would have been
of capon type, with long loose feathers, small comb and wattles, sharp capon's
spurs, and with the temperament of the capon.
The cause of its masculinity was the grafted ovaries. A large grafted
gonad, almost the size of a normal testis, was found attached to the anterior
part of the left kidney on the site selected for grafting. Near this, attached
to the intercostal muscles, was a small amount of gonad tissue about the size
of a pea, and on the corresponding part of the right side was a third small
growth. Multiple growths on the left side could be expected as the ovarian
tissue was usually in several pieces when inserted. These thfee grafts all
showed the same structure, viz., that of testicular tubules in a fibrous stroma.
It differed from normal testis in that the tubules were either immature or
irregular atrophic tubules, and there was much dense fibrous connective
tissue. Normal testis is soft to the touch; normal ovary is lobulated; these
engrafted gonads were smooth and tough and markedly different from normal
gonads.
There can be no doubt that the secondary sexual characters were caused
by the large engrafted gonad. The adult plumage seen in the photograph was
developed when the bird was about 6 months old. It may have been that at
that time there were some ovarian elements present to cause the slight inhibition
of the cocky type plumage, for cystic follicles projected from the surface of
the graft. The comb and wattles and sexual instincts, however, were fully
masculine.
No. 16 (Plate III.) was castrated when 4 days old, and on each side an ovary
from a sister was engrafted. This bird had similar characters to the foregoing,
as can be seen from the illustration. Post-mortem examination showed a
regenerated testis, about one-third normal size, and on the right and left intercostal sites were small ovo-testis like growths. The amount of normal testis
present was sufficient to account for the masculinity of this bird. The grafted
VOL. 11.—NO. 4.
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G. F. Finlay
ovaries proved to be of the same type as those in No. 15, viz., testicular tubules
in a dense fibrous stroma. There can be no doubt that when the adult plumage
of this bird was growing the secretion from the grafted gonads had some
inhibiting effect.
No. 17 (Plate III.) was castrated when 4 days old and about three-quarters
of an ovary of a sister put in the left kidney site. The photograph of this
bird was taken when it was just under 6 months of age, and though the
skeleton had attained full size, the secondary sexual characters were not fully
developed. In general this bird resembled a capon with a small nodule of
testis. Its comb was erect, though but half the normal masculine size for
that age. The plumage did not show greater inhibition than could be expected
for a cockerel of that age. This bird died when 43 weeks old, but apart from
feather growth showed no important change from the photograph.
Examination revealed that it had been completely castrated, and that the
engrafted gonad was but 3 mm. in diameter. It is not safe to draw many
conclusions from this case, but the bird is described, for the grafted gonad
proved to be another case of ovary which contained tubules similar to those
of immature testes. In ill-health gonads, especially testes, become greatly
reduced in size. The evidence that the gonad secretion bears a quantitative
relation to the secondary sexual characters is taken from birds in perfect health
and under standard conditions.
No. 18 (Plate IV.) is a better case but is very similar to the preceding. When
4 days old it was castrated. An ovary of a sister was taken and three-quarters
of it grafted into the left side and one-quarter into the right side. This bird
died when 31 weeks old. The photograph shows it when about 24 weeks old.
In general this bird had cocky secondary sexual characters. It had a black
breast, but the back, saddle, and tail feathers were slightly restricted. The
comb and wattles were about three-quarters full size; but as this bird was
not very strong, this could be expected even if it tad normal testes.
Examination showed that the larger piece of ovary, which had been grafted
into the left kidney site, had grown and was about 1 cm. in diameter. On the
right side there were three small gonad growths, which all together were somewhat smaller than the left graft. These grafts contained testicular tubules of
the same type as that previously described. There was no trace of any of
the bird's original testicular tissue. It should be mentioned that the testicular
growths derived from ovarian grafts are of a very different type to that which
grows from fragments of original testis. The former are tough tissues due to
the large amount of fibrous tissue, while the latter are normal testis growths.
In any case histologically it is not possible to confuse the two types of growths.
There can be no doubt that the masculine secondary sexual characters of
No. 18 were due to the grafts. The slight inhibition of fully masculine plumage
may have been due to some ovarian elements which remained till the time
of moult.
No. 19 (Plate IV.) was completely castrated when 11 days old, and a half
ovary from a sister engrafted into the left kidney site. This bird was quite
healthy till about 5 months old, when it developed partial paralysis. The photograph shows it at 6 months of age. It died from roup when 10 months old.
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Studies on Sex Differentiation in Fowls
Its size was that of a cock. Its spurs were typically cocky. Its plumage,
comb, and wattles were typically henriy. Its temperament was similar to that
of No. 3, that is, it was a peaceful bird unless attacked, when it would reply
with vigour even though crippled. It could not be described as having the
female temperament Post-mortem examination showed what was considered
an ovarian growth of almost full size at the anterior end of the left kidney,
together with what seemed to be one large degenerated yolk. The tissue sent
in for histological examination, however, was not gonad tissue, hence there is
no histological evidence to support this case. However, it was known that
this was a male that had been castrated and received an ovary graft at a stage
later than those cases where the ovary graft changed into testicular tissue. This
bird certainly had the skeleton and spurs of a cock, but the secondary sexual
characters (plumage and head furnishings) of a hen.
Review of Group.—-In reviewing this group let us also
consider the feminised male described in Section 2 of this
paper. Ovaries were grafted into chicks at the following
ages: No. 15 at 2 days; Nos. 16, 17, and 18 at 4 days;
No. 3 at 6 days; No. 19 at 11 days; and the case described
earlier at from 6 to 8 weeks. The ovaries were taken from
sisters (except in the 6 to 8 weeks' old bird) of the same age.
Though the numbers are small it may not be without
significance that the grafts put into chicks up to 4 days of
age changed over to testicular growths, while in those after
this age there was a tendency for the ovarian follicles to persist,
and at times develop full-sized yolks.
That an ovary can develop normally and form full-sized
yolks is seen from No. 3, and that such ovaries have a normal
endocrine function is seen from the first feminised male described
in this paper, also from No. 3, and possibly from No. 19.
It is apparent from the evidence of Nos. 15 and 18 that
an ovary that changes over to a testis develops the endocrine
function of a testis, for the masculinity of these two birds
was due to the engrafted gonad. The slight suppression of
the male plumage of Nos. 15, 16, 18, and possibly 17 was
probably due to some persistent ovarian tissue at the time of
the growth of these feathers. There is nothing remarkable in
this, for evidence will be given later that a gonad can possess
both testicular and ovarian elements at one time, and that
these each have their expected endocrine action.
The feminisation of a male due to a grafted ovary, which
develops and functions as such, is not complete. There is
451
G. F. Finlay
no variation from the normal male skeleton or spurs; but the
plumage and head furnishings (the true secondary sexual
characters) are female.
4. Males with both Testis and Ovary. —This is rather a poor group, but gives
some support to the evidence obtained in the foregoing group.
No. 4 (Plate I.) was thought to be the most typical of this class and
was selected for the coloured illustration. When 11 days old one testis was
removed and half an ovary from a sister was chopped up and grafted into
the left side. As regards size, skeleton, spurs, head furnishings, and sex
behaviour, this bird was typically cocky; but its plumage was intermediate.
On the breast it had a mosaic of the salmon coloured feathers of the female
with the black breast feathers of the cock; while individual feathers were both
black and salmon coloured. The hackles, back saddle, and tail feathers were
intermediate. This bird died from pneumonia when 36 weeks old. The right
testis was normal. The engrafted ovary was attached to the intercostal muscles
and was about 7 mm. square. This amount of ovary was not sufficient to
cause complete hen feathering.
Histological examination showed that although the graft had retained its
typical ovarian structure it was obviously degenerate. All the larger follicles
were in an advanced stage of atresia.
No. 20 (Plate IV.) is an interesting case, but unfortunately the details of the
grafting were not recorded at the time of operation. From its place in the
series, I am able to state that it was n days old when operated on. The
photograph shows it when a year old. It was killed six months later, just after
its second moult. There was no important change in its characters after this
moult Its plumage was almost typically henny, but its saddles were very
slightly tipped, and there was a trace of black in a few of the otherwise salmon
breast feathers. The tail had two slight sickles. My record states that the
pelvis bones were wider and more sprung than in a typical cock; otherwise
its skeleton was typically male. Its comb and wattles did not develop beyond
the pullet size till it was over 6 months old. This bird had very pronounced
sex instincts and outclassed the normal cocks in its masculine advances to
the hens.
When killed, examination showed that it possessed testis nodules on both
the right and left sides—the combined weight of these being 3.5 gms., or
about one-sixth of what the normal healthy cock would have had at this age.
Attached to the right intercostal muscles was an ovary graft about 1 cm.
in diameter, and at the kidney site on the left side was another 0.5 cm.
in diameter. These grafts did not possess any normal oocytes. There
was a proliferation of sex cords with further differentiation into tubules of
immature type.
No. 2 1 (Plate IV.), as can be seen from the photograph taken at about
7 months of age, appeared to be a normal cock. When 6 days old this bird
had the left testis removed and several pieces of ovary from a sister were grafted
in. It died when nearly 10 months old. The testis was very small and weighed
only 180 mgs., while there was only a tiny ovary graft of 30 mgs. This latter
452
Studies on Sex Differentiation in Fowls
was too small to have any visible effect, and the case is included only for the
purpose of showing that this grafted gonad remained an ovary.
Review of Group.—The evidence from these cases tends
to confirm that of the foregoing group. One ovarian graft
was done at 6 days and two at 11 days. The age of the
chicks from which these organs were taken would be the same
as that of the recipients of the grafts. With the exception of
No. 20, these grafted gonads remained as ovaries and showed
no trace of testicular tissue. No. 21 had too small an amount
of ovary to cause any visible hen feathering; No. 4 was
intermediate; while No. 20 was almost completely henny in
plumage.
Female Groups.
1. Females with Testis.—Female chicks were ovariotomised and testes from
brothers or half-brothers of the same age grafted into the kidney site.
No. S (Plate II.) when 4 days old had one testis from a brother put in each
side. As can be seen from the photograph of the body in fig. 3 (Plate VI.),
these testes grew to practically normal size. This bird was of the size and
body shape of a hen. Its bones were small and its pelvis like that of a pullet
before the laying period. Its spurs were of the female type; that is they were
short, blunt, and loose buttons. Its plumage, comb, and wattles were typically
masculine. It developed a short, aborted crow, quite unlike that of a cock.
It was little different from the control hens in temperament. It neither sought
the attentions of the cocks, nor did it make masculine advances towards
the hens.
It was killed when 51 weeks old. Examination showed the large testes
to be normal in structure and containing abundance of motile spermatozoa.
These tended to collect in masses in parts of the tubules, and in cavities under
the covering membrane. The oviduct was infantile. The vasa deferentia
were well developed. These ducts probably persist in all hens, but it is very
difficult to find them in normal hens. In No. 5 they were almost as large as in
cocks. Each was connected with a well-developed epidjdymis. There was no
regeneration of ovary.
No. 22 (Plate IV.) was ovariotomised when 7 days old and four testes from
brothers grafted in—two on each side. This bird developed a somewhat
masculine comb and wattles, otherwise it was like a normal pullet It was
accidentally killed when 6 months old. It had a testis nodule about 8 mm.
in diameter, and a regeneration of ovary about the same size. The oviduct
was quite infantile. One could scarcely expect this small amount of testis to
produce a full-sized cock's comb. The ovary was sufficient to cause normal
hen feathering, but was not sufficient to cause the oviduct to develop beyond
the infantile stage.
No. 23 (Plate IV.) was ovariotomised and four testes from half-brothers
chopped up and grafted into the kidney site. The exact age at the time of
453
G. F. Finlay
operation was not recorded, but it would have been about 6 days of age.
It died when nearly 9 months old. The photograph was taken two months
earlier. Its shape and skeletal characters were those of a pullet, but its
plumage, comb, and wattles were of the normal cocky type. Its behaviour
as far as observed was like that of a pullet
Post-mortem examination showed two nodules of testis growth, the combined weight of which was 0.7 gm. If this bird had lived longer and remained
healthy this would probably have increased to four or five times that weight.
There was a nodule of ovary, about the sue of a pin's head, which had persisted.
The oviduct was infantile.
No. 24 (Plate IV.) when 2 days old was ovariotomised and one testis from
a brother put into the kidney site. This bird was of the same general type
as No. 5 and No. 33. However, there was a slight inhibition of the otherwise
cocky type plumage of the back and saddle feathers, and there were several
salmon feathers in an otherwise black breast. Two photographs of this fowl
are shown on Plate IV. The first shows it at 12 months of age; the second
five months later, just after the moult. It was killed for examination just after
the second photograph was taken.
The engrafted testis was found to be about 2 cm. in diameter, which is
rather under normal size. As was expected there was a regeneration of gonad
from the ovarian site. The base of this growth appeared very like normal
ovary, but there was a projecting new growth almost as large as the testis
graft This new growth consisted of sex cord tissue embedded in a fibrous
stroma and was comparable to the fairly common ovarian tumours. The
oviduct was developing, being about one-quarter full size, or the size of the
oviduct in a 3 months' old pullet
At the time of the assumption of the first adult plumage, that is, about
the fifth month, this fowl probably had but a very small amount of ovarian
tissue, but in the succeeding twelve months sufficient gonad of ovarian type
was evidently regenerated to bring about complete inhibition of the plumage
to the henny type.
No. 25 (Plate V.) was a similar case to the preceding. It was ovariotomised
when 4 days old, and two testes from a brother put in the left side. The
first photograph was taken at is months of age; the second 5 months later.
This fowl is being kept alive for another year if possible. It is quite apparent
that there was a large growth of testis in this bird, and that there was also a
regeneration of ovarian tissue between the first and second moults.
Review of the Group.—These birds were generally considered
to be of the same size as the control normal females, but a
perusal of the actual measurements of various parts of the
body suggests the possibility that the testis grafts had a slight
stimulating effect on bone growth. Case No. 8, to be described
later, also suggests this. However, it can be stated that these
birds had the general skeletal characters of pullets. In fineness
of bone, conformation, spur buttons, and disposition, they did
+5+
Studies on Sex Differentiation in Fowls
not differ greatly from the normal. However, the testis grafts
caused a development of male type comb and wattles as can
be seen from the illustrations better than from the actual
measurements. When ovarian tissue was not present at the
time of the moult the feathers became typically cocky.
a. Females without Gonad s.—No. 6 (Plate V.) was ovariotomised when
2 days old. It is represented in Plate V. at 6 months of age, and in the
coloured illustration at 12 months. At 6 months it appeared very much
like a capon, except that it was much smaller and had finer bone. The
feathers were of the long, loose type which develop on castrated males. The
comb was rather too large for a typical capon and showed evidence of gonad
activity. Its skeleton and body shape was very similar to that of a pullet;
while the male capons had larger bone, prominent spurs, and narrower pelvis.
The stance of No. 6 was much the same as that of the normal pullets.
At 12 months of age this bird was killed. A small right gonad about
0.5 mm. in diameter was found and this proved to be testicular tissue. Thislatter accounted for the slight comb development, and without doubt accounts
for the rather more compact plumage at 12 months than at 6 months of age.
This bird was very thin, and it was possible to note that vasa deferentia were
present. The oviduct was infantile.
No. 26 (Plate V.) was an interesting case. It was ovariotomised when 7 day*
old. When full-grown this bird grew feathers which were mostly henny; but instead
of a pure salmon coloured breast, there was a mosaic of salmon with brownishblack feathers; also the back feathers were very slightly tipped. At 11 months
of age, when the photograph was taken, the comb and wattles were much larger
and coarser than in a normal hen. They were almost masculine, but drooped.
On examination it was found that the left ovary had been completely
removed and there was no regeneration on that side; but the right gonad had
developed into an ovo-testis about 13 mm. long by 3 mm. broad. There was
good evidence of both ovarian and testicular endocrine activity. The oviduct
was the size of that of a 3 months' old pullet.
No. 27 (Plate V.) was ovariotomised when 2 days old, but there was
ovarian regeneration, and this bird became a typical pullet except that it
had masculine type spurs. This is an exceptional case of cocky spurs in
a female and probably has no relation to gonad activity.
Review of Group.—In the two cases in which the left ovary
was entirely removed, the degenerated remnant of right gonad
was reactivated and developed to a slight extent. In the first
case this right gonad became a testis and thus supports the
numerous cases described by other workers in which the right
gonads of ovariotomised fowls became testes. The second case
shows, however, that the right gonad has the potentiality of
developing either as a testis or ovary.
455
G. F. Finlay
3. Females with Ovaries.—No. 7 (Plate II.) and No. 28 (Plate V.) are given
as typical Brown Leghorn pullets. The pictures were made when they were
47 weeks old and in laying condition. It should be noted that the comb
and wattles in pullets remain rather small until the birds are about six months
of age or when the laying period approaches. These organs then grow rapidly
but usually hang down.
4. Females with both Testis and Ovary.—There are three interesting cases to
record in this group, each one showing some peculiar feature.
No. 8 (Plates II. and V.) when 7 days old received two testes from a
brother; part being put subcutaneously at the side of the body. This bird
showed the effects of the testes from about 3 months of age The comb
developed to almost the same extent as in the normal males. This can be
seen from the photograph on Plate V. which was taken when the bird was
under 7 months of age, and when the combs of the control pullets were quite
small. The comb was of this relative size from about 3 months of age onwards.
The coloured illustration represents the fowl in laying condition at 10 months
of age. The plumage could not be considered as being typically henny.
The tail feathers were slightly masculine, while there was a reddish coloration
over the body which was not typical of the controls. This bird laid normally,
and one egg which was incubated proved to be fertile—the fertilisation of
course being effected by a cock.
When killed two testis grafts were found in the body cavity, both showing
motile sperm. There were also two small nodules of testis in the subcutaneous
position. The combined testis tissue was rather less in amount than in
a single fully developed testis. The ovary and oviduct were quite normal.
This case shows that testis can cause comb growth of a cocky type even
in the presence of an ovary. As regards the plumage it is difficult to give
an interpretation. Either the testis has some stimulating effect on plumage,
or else the ovarian action is inhibited to a slight extent in the presence of
testis. The former hypothesis is probably correct, for there was no evidence
of inhibition as regards development of the ova, oviducts, or sexual instincts.
The two following cases tend to support this view.
No. 29 (Plate V.) had about one-half her ovary removed when n days
of age. One testis from a brother and one from a half-brother were grafted
into the left kidney site, and one from a half-brother into the right. The
dissection of the body, seen in fig. 4, Plate VI., shows the one testis
which grew.
This bird had a strong comb and wattles, tending towards the masculine
type, otherwise it was typically henny. It laid before it was killed. Postmortem examination showed a single testis graft, about 2 cm. in diameter, on
the left side. The ovary was normal and a yolk was found entering the left
oviduct This case is also of interest because of the persistence of the right
oviduct, in addition to the normal left one. This of course was not in any
way due to the grafting, but is an illustration of a not uncommon occurrence
in fowls.
No. 30 (Plate V.) when 4 days old had about three-quarters of its ovary
removed and one testis from a brother put in each side. This bird had plumage
45 6
Studies on Sex Differentiation in Fowls
of an intermediate type, while its comb and wattles approached the cocky type.
As regards its secondary sexual characters it showed only slight ovarian action.
It had the disposition of a hen.
The body is depicted in fig. 5 (Plate VI.), from which it can be seen that
there were two testes of almost normal cocky size growing at the site of grafting.
The ovary was small and had no large yolks. It is difficult to account for this
failure of the ova to mature, but the case suggests that perhaps the great amount
of testis present may have been unfavourable for the ovary. In the cases
previously described where the ova developed to maturity there was relatively
less testis present. The oviduct was fully developed; and this suggests that
the endocrine function of the ovary was not inhibited by the testis. I think
that if this bird had no testis graft, that even the quarter ovary would have
sufficed to cause hen feathering. The intermediate plumage may be evidence
of a stimulating effect of the testis rather than a lack of inhibition on the part
of the ovary.
Review of the Group.—In all three birds the testis grafts
caused masculine head furnishings. They also probably caused
some stimulation of the plumage, for No. 30 with large grafts
had intermediate plumage ; No. 8 with a smaller amount was
only slightly different from a normal hen ; while No. 29 with
the smallest graft had normal female plumage. The small
inactive ovary of No. 30, however, may not have been as
effective as a larger ovary would have been. Apart from the
masculine head furnishings and the plumage difference, these
birds were typical pullets.
Comparison of the Eight Experimental Groups.—One of
the most striking points in these studies was that certain sex
differences were unaltered. Normal male and female Leghorns
are characterised by marked differences in size, body shape,
spurs, and mentality, and as regards these characters, transformation could not be effected by gonad grafts.
The upright stance of the cock is the most favourable
posture for balancing properly. He is narrower and lighter in
the pelvic region, and carries heavy head furnishings in front.
When a heavy comb and wattles do not develop, as in the capon,
the bird tends to assume a more horizontal stance ; while a
female tends to adopt the more upright position if it possesses
masculine head furnishings. While, therefore, the normal male
and female have a markedly different stance, it is possible to
greatly modify this character until there is little difference.
The fundamental shape and general skeletal characters were
457
G. F. Finlay
little altered if at all by the gonad grafting. The size differences
between the sexes remained very distinct, though it may be
considered that the measurements given in the table indicate
that the presence of testis in a female slightly increases bone
growth. However, as can be seen from the coloured illustrations
(and also the photographs), which show the relative sizes of
the birds as far as possible, there are two main size groups—
male and female. Spurs are not secondary sexual characters.
They were not greatly altered by endocrine variations. The
males had cocky spurs whether they carried testis or ovary;
while the females had the small loose buttons whether they
had ovary, testis, or both types of gonads. Apparently the
only variation from normal was in the capon class. These
birds invariably developed very sharp, long spurs. It may
be that these are ordinary cocky type spurs which are not
worn blunt, because the capon is lazy and does not actively
scratch for food or fight; however, I am inclined to the view
that one factor causing this spur growth is the absence of
gonad secretion. If the latter is true then it would indicate
that in this respect the ovarian graft in the male is just as
potent as the normal testis. However, in the female neither
testis nor ovary causes the cocky type spurs to develop. If
these birds had been kept alive longer, no doubt better evidence
on spur growth would have been obtained.
There can be no doubt there was a fundamental psychological difference between the sexes. The male with ovary
still had the mentality and temperament of a male; while the
female with testis grafts still had female instincts. The pyschological state was of course modified to a certain extent by gonad
activity; but it was impossible to develop the mental qualities
of a male in a female or vice versa.
The castrated male differs from the normal cock in the following characters : he has undersized comb and wattles; feathers
are longer and less compact ; he lacks the mental stimulation,
aggressiveness, and pride of the cock and hence does not fight;
he is lazy, contented, and therefore readily fattens, while his
spurs grow long and sharp; he will sometimes crow with an
undeveloped voice, but he lacks the incentive to do so ; his vasa
deferentia do not enlarge; in short, he lacks those characters
458
Studies on Sex Differentiation in Fowls
which develop in response to the stimulation of the hormone
of the testes.
The male that has had his testes replaced by ovary remains
masculine as regards size, skeletal characters, spurs, and basic
mentality. However, he develops female plumage ; female comb
and wattles ; and while he does not develop the domineering
spirit or crow of the cock, he has a sex stimulation which causes
him to be more active than the capon and bolder than the hen.
The group of males with both testis and ovary was rather
small, but there was good evidence that such birds differed
from normal males only in that their plumage tended to be
inhibited towards the female type.
The females which had their ovaries replaced by testis
grafts remained female in body shape, skeletal characters, spurs,
voice, basic mentality, while in size they remained in the female
group though possibly slightly modified as regards bone growth.
The oviduct remained infantile. The assumed perfect male
plumage, comb, and wattles, and the vasa deferentia developed.
Their instincts for the most part appeared henny. At times
they gave voice to a short, henny crow; but they did not tread
hens, or show any rivalry towards the males.
The group of ovariotomised females, though small, gave
evidence that in the absence of ovary in the female, plumage,
comb, and wattles, similar to that in male capons develop.
They retain the skeletal characters, body shape, and mentality
of females. The remnant of the right ovary may develop into
a small functioning gonad. In one case it became a testicular
growth ; in another it became an ovo-testis with a dual endocrine
function.
The females with both testis and ovary showed the effect
of the testis only in the masculine development of head
furnishings, and in a tendency to tipping of the plumage.
In No. 30 the great amount of testis may have had something
to do with the failure of the ovary to produce full-sized yolks.
Otherwise these birds were normal females.
For comparison of the experimental birds a Table of
Measurements is given. Unfortunately no very satisfactory
method of measuring size differences could be devised, but
there could be no doubt as to the marked size differences
459
G. F. Finlay
TABLE OF MEASUREMENTS
6 S
+ T.
I
9
10
...
11
n
Experimental Group.
No. of fowl .
Age in days
at
i i Castrated.
Age in weeks when 48 52 52 49
mciuurcu
4tt 4ft 3tt 4tt
Weight in lbs.
Length of body • . 51 5° 46 50
Wing spread *
Shank length
53
s
52
10
12
M
7
3
3
4
3
6
52
50
51
5i
47
4t«
49
54
13
4ft
15
16
17
2
4
52
5'
4A 4*8 3tt
51
49
52
53
52
53
11
18
'9
4
4
11
43
3'
46
4 & 2A
3A
49
47
49
50
49
49
51
50
53
52
47
55
11
11
11
12
12
12
12
12
12
Shank circum.
4-8 4-8 4-4 4-8
4-8
4-8
4-8
4-4
Middle toe 4 .
51
5'i
5-i
57
5-4
5-4
5-'
5-i
4-8 4-4 4-4 4-1 3-8 4-4
5-4 5-i s-i 5-4 6 5-4
29
28
26
29
30
29
28
29
28
i
<?
$
s
$
•
Spurs .
Stance .
Q
Plumage
£
Q
Comb length
14
16
14
Comb depth .
8
9
9
Wattles depth
9
9
Wattles width
7
6
7
7
Behaviour * .
<? $
capon capon capon capon
c?
$
$
<?
6
i+
capon capon capon capon
27
Q
Q
Q
6
28
30
Q
$
Q
s
(?
3°
Q
?
c?
Q
?
10
7
3-8
3-8
'3
8
4
12
4
8
14
14
9
2
7
4
2
5
8
5
9
6
2
6
3
2
4
7
9
8
4
...
3
5
4
3
4
5
6
4
...
...
...
8
<?
3'5
...
1
c?
29
$
T growths frotn 0 grafts.
..
4 mm. diam. C) nodul
Leg
6
12
53
n
51
12
2
11
6 i Castrated + 0.
Complete castration.
Nodule of T.
Nodule of T.
Complete cast ration.
Normal T.
O = ovary
Normal T.
T = testis
Normal T.
Remarks as to
gonads found
Subcutaneous T graft
01
0 grafts with yolks
nodule.
Growth T froi
nodule reg<
Nodule regen.
from
O graft.
H
r
Linear measurements in centimetres.
1
From tip of beak to end of tail (feathers excluded).
- Feather* excluded.
3
From outer angle tibio-taraal joint to ball of foot
460
1 H
& . H+
c d
O
Studies on Sex Differentiation in Fowls
OF EXPERIMENTAL FOWLS.
9 t Ovariotomised + T.
9 9 Ovariotomised.
28
8
29
3O
2
...
7
II
4
51
47
47
47
52
51
3i?
4
3A
3A 3tt
4
4A
42
45
48
43
46
44
46
43
46
20
21
5
22
23
24
25
6
26
27
II
II
6
4
7
6
2
4
2
7
36
52
38
51
26
37
51
51
52
48
2tf
5A
3
3tt
...
...
...
...
...
...
2A
3-8
51
5'7
5-i
3-5
4-8
3-8
3-8
3-8
4-1
3-8
4-1
4-8
4-8
4-4
3-8
4.4
3-8
3-5
3-8
4.4
4-4
4-8
4-8
4-4
22
23
23
26
23
24
L. (J
R. 9
3
+0
+0
24
6
10
...
...
10
5
5
4
4
3
3
<S
H
H
...
24
9
3
Q
Q
3
capon
11
4
3
9
3
9
3
9
9
3
II
12
10
8
6
6
4
6
4
6
5
...
9
12
6
10
6
6
4
8
6
5
5
6
4
5
3
4
4
7
6
5
5
S
3
5
3
4
4
5
4
9
9
graft + regen.
graft 4- tiny 0.
graft + regen.
ot killed yet
d
large T grafts.
0
25
capon
0+
6
10
24
0+
6
6
6
25
3-5
4-8
0+
6
5
9
6
5
4-3
...
+ tiny 0 nodu le.
10
10
3
+ 0 grafts.
14
9
3
3
+ 0 graft
12
9
0+
S
9
9
CM-
3
&
3
$
3
24
9
0+
3
30
9
CM-
<J
29
9
CH
3°
10
M
H
H
H
2
1
d
i
O
O
tn
O
O
O
Linear measurements in centimetres.
4
To base of claw.
From proximal extremity of tibia to base of claw of middle toe.
• Only indicated when typical <J or 9 .
5
VOL. II.—NO. 4.
47
+ large T graf
4-8
47
10
normal + T gi
4
44
10
+0
9
47
44
normal + T gr
13
47
•10
45
•to
45
12
43
+0
50
12
45
+0
55
43
46
47
t gonad — ovo-testi
51
45
M 3A
t gonad - T.
51
...
40
+0
47
46
9 9 + T and O.
7
...
4
2 ^
9 9 Hr O .
•to
T and 0.
+0
o* <5 +
2G
G. F. Finlay
between the male group on the one hand and the female
group on the other.
Except in the case of testis in full activity, it was not
possible to form an estimate as to the endocrine capacity of a
gonad in relation to its size.
5. Discussion.
Various authors have attempted to classify the characters
relating to sexual differences into definite categories, and
particularly to define what are the secondary sexual characters.
In the foregoing descriptions of cases I have endeavoured to
avoid any very rigid classification. I recognise that there are
certain primary differences between the sexes which occur
independently of the gonads. In these one could probably
list a marked difference in size, skeleton, spurs, mentality, voice,
and the presence in the female of an oviduct which is absent
in the male. Then the hormones of the gonads cause further
differences to arise in normal birds, these being in the plumage,
comb, wattles, and ear lobes, and also probably in the persistent
Wolrfian ducts. For the reasons that these latter characterdifferences do not appear in the absence of gonads and that
both sexes are equipotential as regards their development, they
are rightly regarded as secondary sexual characters. However,
the gonads exercise some influence on most, if not all, of the
primary character differences. The oviduct is markedly altered
in size and function in response to ovarian activity; the
mental qualities or instincts become more marked; the voice
develops; while bone and spur growth is possibly slightly
modified.
It is apparent then that it is somewhat difficult
to make a rigid classification of these characters.
Zavadowsky, who has carried out a parallel series of
experiments, though with older chickens, differs in some of his
conclusions. He claims that the sexes are equipotential as
regards their characters. However, the fact that his birds
were several weeks old before they were operated on makes it
difficult to draw conclusions as to those primary differences
which must have been quite marked at the time of operation.
He regarded the castrated male as being similar to the
ovariotomised female if the operations were complete. He
462
Studies on Sex Differentiation in Fowls
found, however, as have others, that when the ovary of a
pullet is removed, the remnant of right gonad tends to develop
as a testis, and he terms this the heterosexual potency of the
right gonad.
Petard evidently agrees with Zavadowsky as to the equipotentiality of the sexes. He found that ovariotomised females
tended to develop towards the male type. This was doubtless
due to the growth of testicular tissue from the right gonad site.
Further, Pezard shows that in one case at least, a female
which had been ovariotomised and had received a testis graft
developed male characters and behaved like a true cock.
However, there was an interval of several years between the
operation and the observation, and it must be realised that
old hens not infrequently show some masculine tendencies.
The testis graft would tend to emphasise this tendency. In
my own series I found that the females with testis differed
in important respects from the males with testis, and while I
am prepared to admit that it is not safe to draw too many
conclusions from the relative size and conformation of these
birds, yet the marked differences in instincts, behaviour, voice,
and spurs forces me to the conclusion that the sexes are not
equipotential. A comparison of my control females with the
feminised males also supports this claim.
Morgan states that if a piece of testis is left and grows in
the body cavity after a castration operation, the size of the comb
is a fair index of the size of the testis nodule. In my own work
1 found that in the imperfect capon class where the birds had
an intermediate comb development, one could form a very fair
estimate of the size of the testis nodule which conditioned such
comb growth. This is rather opposed to Pe'zard's view that
with a certain minimum of testis, all the secondary sexual
characters develop without fractional degrees of development
(the "all or none" law).
These operations on chicks were performed as early as
2 days of age. Greenwood went still further and grafted
gonads on to the chorionic membrane of embryos as early
as the seventh day of incubation. He found that testis grafts
grew normally in female embryos and ovary grafts in males.
The development of the embryos' own gonads or its accessory
463
G. F. Finlay
ducts during embryonic life was not affected. It is then interesting to ask : what is the significance of the fact that some of
the ovary grafts described in this paper developed as testicular
tissue and that the right gonad, when stimulated by ovariotomy
of the left, generally grows into a small testis nodule ?
The gonads commence to differentiate at the seventh day
of incubation. The testes seem remarkably stable, and no
evidence has yet been brought forward that these organs ever
change the course of their development from embryonic life
to sexual maturity. Ovaries taken from chicks up to 4 days
of age, however, and grafted into males (with or without testis)
developed as testicular growths with a testicular endocrine
function. With one exception, ovaries grafted at a later age,
that is from a six-day chick on, developed as ovaries when
grafted into males. From these cases alone it is not clear
as to what causes this result. But from all the evidence that
has been put forward by various workers that in ovariotomised
hens a testis generally develops on the right ovarian site,
it would appear that any sex cords that are proliferated at
that late stage, differentiate into testis tubules. Greenwood
shows clearly, however, that the right gonad is not fundamentally
different from the left. That this differentiation into testicular
tissue is not restricted to the right gonad is seen from case
No. 24, in which in regeneration of the left gonad following
ovariotomy an ovo-testis developed. No. 25 is almost certain to
be a similar case. Also in a number of cases of females developing certain male characters described by Crew, and also similar
ones by Boring and Pearl and others, there was evidence that
in a proliferation of new gonad tissue in the left ovary the sex
cords differentiated into testis tubules rather than into ovarian
tissue. This evidence suggests that even in the female body,
whether in the presence or absence of testis, that sex cords
proliferated after the embryonic stage do not meet the stimulus
necessary to cause a differentiation into ovarian follicles.
Greenwood shows that the presence of a testis graft in a
female embryo does not interfere with the differentiation of
the embryo's own ovary and Miillerian ducts. This certainly
suggests that the specific stimulus which causes gonad differentiation is a function of the embryonic soma, and that shortly
464
Studies on Sex Differentiation in Fowls
after hatching this environment favourable for typical differentiation no longer exists.
How then, can one account for the fact that certain ovarian
grafts in males became testes, while others developed normally
as ovaries ? As a provisional hypothesis I would suggest that
in the younger cases, the germinal epithelium was possibly
more active and, owing to the small size of the ovary at that
stage, the oocytes were damaged during the operation. Hence
the graft would represent new growth from the germinal
epithelium, but the sex cords not meeting the female embryonic
environment differentiated into the more stable testis. From
6 days of age on the ovary has increased in size and can be
removed from the chick with less damage than when newly
hatched. Then when this gonad is grafted into a chick its
oocytes continue to develop normally in whatever endocrine
environment they find themselves.
6. Conclusions.
1. There are a number of primary differences between the
sexes in fowls, which are not conditioned by the gonads. These
are: size, conformation, spurs, the presence of an oviduct in
females but not in males, voice, and pronounced psychological
differences.
2. Some of these characters are modified by gonad activity,
but the fundamental differences cannot be obliterated by
masculinisation or feminisation experiments.
3. Castrated birds of both sexes are of a neutral type as
regards plumage and head furnishings. The feathers, while of
the general type and colour of the cock, are longer and less
compact. If testis is present as the sole gonad tissue, both
sexes develop perfect cocky plumage and head furnishings. If
ovary is the gonad, however, both males and females develop
henny plumage and henny head furnishings. If both testis
and ovary are present in either sex, each gonad has its specific
endocrine function, and there is no neutralisation of the one by
the other. The testis causes a strong, erect, cocky comb to
develop in the female as well as in the male ; while the ovary
tends to inhibit the plumage towards the henny type. However,
this inhibition of the ovary is not complete in the presence of
VOL 11.—NO. 4.
465
2G 2
G. F. Finlay
testis, for in these experimental hermaphrodites there was some
lengthening or tipping of the feathers and a more reddish
coloration than is present in typical henny plumage. As
regards these secondary sexual characters there is therefore
equipotentiality of the sexes.
4. The more fundamental sex characters do not follow the
gonads as do the foregoing secondary sexual characters. In
masculinisation of the female (replacement of ovary by testis)
the size, conformation, and instincts are only slightly modified.
In feminisation of the male (replacement of testes by ovary)
the bird retains the size, conformation, spurs, and mental
qualities of the male. In the female with both ovary and
testis, the bird is typically henny as regards these primary
sex characters; while the male with both types of gonads is
typically cocky. One is therefore justified in stating that as
regards these primary sex differences there is not equipotentiality of the sexes. In other words there is a definite
sexuality of the soma.
5. While the gonad does not condition primary sex
differentiation, but only accentuates the differences determined
by the zygotic constitution of the individual, the sex constitution
determines what type of gonad shall grow. The specific
determining stimulus is present during embryonic life; later
than that, if sex cords are proliferated from the germinal
epithelium, even in females, they differentiate into testis
tubules.
6. The testis seems remarkably stable. Once it is differentiated as such, it always develops as testis; and from
numerous cases of regeneration from fragments, it was apparent
that such new growth followed a normal course of development
as testis.
7. The ovary is more unstable and even after differentiation
may change over and develop testis tissue with normal testicular
endocrine function if it is subjected to an abnormal environment.
The new tissue is, however, probably derived from a late
proliferation of sex cords, which, failing to receive the specific
stimulus which is present in female embryos, develops into
irregular testis tubules.
8. The right gonad of the female, which degenerates during
466
Studies on Sex Differentiation in Fowls
embryonic life, is represented at hatching by a scarcely visible
fragment of tissue. This fragment or the adjoining germinal
epithelium may give rise to ovarian or testicular growths
according to the environment. Previous workers, ovariotomising at a relatively late age, found that this caused a
testicular growth to appear on the right ovarian site. A bird
which was ovariotomised at 7 days of age, however, developed
both ovarian and testicular tissue in the right gonad. It is
possible that the ovarian part represented the fragment of
already differentiated ovary which persisted at the time of
operation, while the testicular tissue represented a new growth
after the embryonic female stimulus had disappeared.
9. The accessory genital ducts react to hormonic stimulus
as follows: In both male and female the Wolffian ducts persist
after hatching, and in the male become the vasa deferentia.
This development is due to the stimulus from the testis
secretion, for when testis is present in females as well as males
the vasa undergo this secondary enlargement; while when testis
is absent from either sex they remain infantile. These ducts
are apparently not affected by the presence of ovary. The
Miillerian ducts are usually represented in post-embryonic life
by the single left duct which develops as the oviduct. Both
ducts persist in rare cases and develop normally.
The
secondary enlargement of the infantile duct to the functioning
oviduct is conditioned by the ovarian secretion. Testis does
not interfere with the development or normal functioning of
this organ. If ovary is not present the oviduct remains
infantile. When small amounts of ovary exist there is a
varying degree of development of the oviduct, indicating a
quantitative relationship between hormone and organ.
10. Gonads can grow and function normally in either sex
and in any combination. In the male the engrafted ovary
forms yolks as in the laying hen. In the female testis develops
and performs its function of producing motile sperm just as in
the cock. Grafting inside the body cavity seems to give better
results than subcutaneously, probably due to the protection and
vascularity of the former position. There is apparently no
incompatibility of the gonads or their hormones. Both show
the specific effect on the various tissues and functions which
467
G. F. Finlay
are susceptible to their stimulation; while with feather
characters and possibly some other characters, which are
affected by both gonads, each hormone has a visible effect,
resulting in a blend of the characters.
ii. The evidence shows that there is a quantitative relation
between testis or ovary on the one hand and the degree of
development of certain organs on the other.
7. References.
Boring, A^ and Pearl, R. (1918), "Sex Studies. X—Hermaphrodite Birds," Jourrt.
Exp. Zool., 26.
Crew, F. A. E. (1923), "Studies in Intersexuality. II—Sex Reversal in the Fowl,"
Proc. Roy. Soc., B, 96, 256-78.
Domm, L. V., " Sex Reversal following Ovariotomy in the Fowl," Proc. Soc. Exp.
Btol. and Med., 22, No. 1.
Fell, H. (1923), "Histological Studies on the Gonads of the Fowl. I—The Histologidal Basis of Sex Reversal," Brit. Journ. Exp. Bio/., t, 97-130.
Goodale, H. D. (1916), " A Feminised Cockerel," Journ. Exp. Zool., 20.
Goodale, H. D. (1916), " Gonadectomy," CarntgU Inst. Wash. Pub., No. 243.
Goodale, H. D. (1916), "Further Developments in Ovariotomised Fowls," Biol.
Bull., 80.
Goodale, H. D. " Feminised Male Birds," Gtnetics, 8, No. 2.
Greenwood, A. (1925), "Gonad Grafts in Embryonic Chicks and their Relation to
Sexual Differentiation,0 Brit. Journ. Exp. Biol., 2, 165-78.
Morgan, T. H., "Secondary Sexual Characters," Carnegie insU Wash. Pub.,
No. 285.
Pe'zard, A. (1918), " Le conditionnement des caracteres sexuel secondaires chez
les Oiseaux," Bull. Biol. France et Belgique, Paris, 1.
Pe'zard, A. (1922), "Modifications peViodiqtie ou definitives des caractere sexuels
secondaire et du comportment chex les Gallinaces," Annalcs des science
naturelles, zoology, io* serie, 6, 83-104.
Pe'zard, A. (1922) " L a loi du 'tout ou rien' et le gynandromorphism chez les
Oiseaux,"/. dephysiol. et depatkol,generate, 20, 495-508.
Pe'zard, A. (1922), " La loi du ' tout ou rien' et le gynandromorphism chez les
Oiseaux. Le gynandromorphisme endocrinien," Ibid., 20, 495-508.
Pezard, A., Knud Sand, and F. Caridroit (1923), "Production experimentale du
gynandromorphisme chez les Oiseaux," C. R. Acad. Set'., 176, 615-18.
Zavadovsky, M. (1922), Sex and the Development of Sex Characters, Government
Publication, Moscow (in Russian with a German summary).
468
STUDIES ON SEX DIFFERENTIATION IN FOWLS—G. F. FINLAY
PLATE I
MALE GROUP
t. Normal male.
3. Male castrated and with ovary engrafted,
2. Castrated male.
4. Male with both ovary and testis.
STUDIES ON SEX DIFFERENTIATION IN FOWLS—G. F. FINLAY
PLATE II
8
FEMALE GROUP
5. Female ovanotomised and with testes engrafted.
7. Normal female.
6. Ovariotomised female.
8. Female with both ovarv and testis
STUDIES ON SEX DIFFERENTIATION IN FOWLS—G. F. FINLAY
PLATE III
STUDIES ON SEX DIFFERENTIATION IN FOWLS—G. F. FINLAY
PLATE IV
STUDIES ON SEX DIFFERENTIATION IN FOWLS—G. F. FrNLAY
PLATE V
STUDIES ON SEX DIFFERENTIATION IN FOWLS—G. F. FINLAY
PLATE Vf