As has been mentioned in the Introduction, the
literature on the reproductive tract of sheep is voluminous.
The oestrous cycle and the cyclic changes in the reproduc¬
tive tract of the ewe have been studied by many
investigators for different purposes. The study of the
placenta of sheep also received much attention due to the
unique position of the cotyledonazy placenta in the
classification and evolution of the mammalian placentae.In this study the morphological and histochemical
changes in the oviducts, uterus and placenta of sheep,
during the oestrous cycle and pregnancy, have been further
investigated and new histological and histochemical
observations have been added. Use of the electron micro¬
scope, freeze-drying and freeze-substitution techniques
were of great advantage in the present study.The material was taken from thirty-nine non-pregnant
and fifty-four pregnant sheep of Scottish breedsj fourteen
specimens of pregnant animals were of known history and
the rest, of unknown history, were collected from the
Edinburgh abattoir.The changes in the oviducts during the oestrous cycle
have been described in the text and have more or less
confirmed the findings of previous authors. The tubal
epithelium was found to be in a phase of growth during
pro-oestrum and by the onset of oestrous to be in a phase
of secretory activity, which gradually diminished towards
the end of the cycle.There were no marked changes in the oviducts during
pregnancy and the author could find no reference to the
morphology and the fine structure of the oviducts of
pregnant sheep. In the present study, the fine structure
and changes in the tubal epithelium of the pregnant ewe
have been described; the epithelium was found to be
quiescent and many cells were degenerating during the
greater part of the pregnancy period. Only towards the
end of gestation did any activity appear in the epithelial
cells. The ultrastructure of the tubal epithelium
revealed that it consisted of ciliated and non-ciliated
columnar cells in alternating groups. It also showed that
the ciliated cells are non-secretory and possibly have an
absorptive function since they possess microvilli.The histochemical investigation showed that the
active tubal epithelial cells are rich in carbohydrateprotein
complex substances. They also contain ribonucleic
acid, lipids and acid phosphatase. Alkaline phosphatase
was found only at the free borders of the cells and iron
was also demonstrable in traces along the cell borders.
The cyclical variation in the quantity and distribution of
these substances within the cells has been described in
the text and the secretions of the oviducts were considered
to be mainly carbohydrate-protein complexes, i.e. glyco¬
proteins or mucoproteins. The significance of the other
chemical substances found in the tubal cells and the lumen
of the oviduct was discussed.The uterine changes during the oestrous cycle were
described. It has been observed that the cyclical changes
in the uterus follow closely those of the oviducts. The
endometrium showed a period of growth preceded by
vascularisation during pro-oestrum, a period of secretory
activity during metoestrum and early dioestrum, and,
finally, a period of regression and infiltration of leucocytes towards the end of the cycle. The present
observations have largely agreed with the findings of
previous authors. In the endometrial stroma melanocytes
were encountered in some of the specimens collected and
were considered to be of no physiological value. Other
lymphocyte-like cells containing important chemical
substances were encountered in the subepithelial layer and
around the uterine glands; these have been discussed in
relation to similar cells in the gravid uterus.The uterine and glandular secretions have been
studied histochemically and found to be rich in a variety
of important chemical substances. The cells of the
uterine and glandular epithelium showed the presence of
ribonucleic acid, lipids, inorganic iron and acid phos¬
phatase; alkaline phosphatase is active only at the free
borders of the cells. The histoohemical reaction at the
free border of the uterine epithelium and in the lumen of
the uterus and the ducts of the glands showed the presence
of a carbohydrate-protein complex substance. Accordingly,
a possible relationship between the phosphatases present
at the free borders of the cells and the mucoid substance
found outside the cells was suggested and discussed.The study of the morphology and histochemistry of the
gravid uterus and placenta of the ewe was a major part of
the present investigation. The changes in the gravid
uterus and the development of the placenta have been
described in the text at different stages of pregnancy.
The condition of the uterus before implantation of the
blastocyst was found to be similar to that of early
dioestrous, i.e. the endometrium was in the active phase.
When the blastocyst came in contact with the endometrium,
the uterine epithelium was destroyed at the sites of
contact and before the end of the first month of gestation
the blastocyst had increased enormously and the endometrium
was denuded of its lining epithelium in most of the
caruncular and intercaruncular areas.The destruction of the uterine epithelium and some of
the endometrial stroma of the caruncles was considered to
be due mainly to an ingrowth of dark staining binucleate
cells of the trophoblast which migrated to the maternal
side and possibly were aided by other chorionic cells.
Thi3 destruction was believed to be caused by some process
of digestion and absorption but not by true phagocytic
action because the dark staining binucleate cells frequently
seen nearest to or within the degenerating maternal tissues
were apparently non-phagocytic.In the present study the formation of the foetal
villi and the maternal crypts in the sheep's placentome
have been described. It was found that the crypts
developed before the primitive villi were formed. The
histological evidence showed that the maternal tissues had
degenerated in the form of tracks vertical to the surface
of the caruncle, the degenerative tissues eventually
disappeared and then folds of chorionic epithelium or
primitive villi entered the evacuated ciypt3.The fine structure of the junctional zone of a fully
differentiated placentome was examined under the electron
microscope and it was found that the foetal and maternal
lining cells possess apical microvilli which were interdigitating
with each other except where debris and
secretory granules had intervened. Intracytoplasmic
inclusions were found in both foetal and maternal cell3j
the former showed characteristic large vesicles near the
microvilli while the latter showed characteristic electron
dense granules.The histochemical reactions showed that glycogen
granules were present in the walls of the foetal and
maternal blood vessels. The columnar chorionic cells at
the bases of the villi contained glycogen. They contained
inorganic iron which is believed to be liberated by the
phagocytosed red blood corpuscles. Lipid droplets were
also found towards the bases of these cells. Acid and
alkaline phosphatases, lipids and ribonucleoproteins were
observed in greater quantities in the syncytial lining of
the maternal crypts than in the chorionic epithelium.In the light of the present observations and the
findings of other authors, the syncytial lining of the
crypts being of foetal origin, the foetal-maternal
relationship in the placentome of the ewe is believed to
be a syndesmochorial one. The phosphatases and lipids
in the binucleate cells and the syncytial lining were
considered to be of vital importance in the transfusion of
substances across the placental membrane.In the intercotyledonary areas of the sheep's
placenta, the uterine epithelium was eroded in the places
which were in contact with the blastocyst during early
pregnancy excepting that around the glands and at the
junctional zone between the caruncular and intercamncular
areas and the tapering parts of the horns. The epithelium
was believed to be destroyed by a similar process to that
described in the caruncular areas. However, the uterine
epithelium was restored in the intercotyledonary areas
after the second month of pregnancy, and the foetal maternal relationship had eventually become an epitheliochorial
one. The chorionic epithelium in apposition to
the openings of the uterine glands wa3 thickened and
invaginated giving rise to depressions known in the pig's
placenta as "areolae". The uterine milk and debris were
found in the spaces between the areolae and the openings
of the glands.The uterine glands increased in length and complexity
and they were of wide diameter and functional throughout
pregnancy. The histochemical reactions showed that a
copious flow of secretion was poured out by the glands.
The epithelial and glandular cells contained ribonucleic
acid, acid and alkaline phosphatase, lipids, and inorganic
iron.lymphocyte-like cells containing intracytopla3iaic
granules were observed within the uterine and glandular
i epithelium of pregnant ewes. The granules were
eosinophilic PAS positive, stainable by pyronim Y, i.e.
containing ribonucleic acid, and showed alkaline phos¬
phatase activity. The similarity and relationship between
these cells, the lymphocytes of the endometrial stroma
and the plasma cells were discussed.Large round cells containing pigments, PAS positive
material, phosphatases and ribonucleic acid, were observed
in the endometrial stroma of pregnant ewes and these cells
were considered to be macrophages of the endometrial
connective tissue
