The development of the cornea is a fascinating process. Its dual origin involves the
differentiation of surface ectoderm cells and the migration of mesenchymal cells of
neural crest origin. This research aimed to demonstrate the morphogenesis of the
rabbit cornea from fetal to postnatal life using light- and electron microscopy, and
immunohistochemical analysis. There were 27 rabbit embryos and nine rabbits used.
The rabbit cornea begins its prenatal development on the twelfth day of gestation.
The surface ectoderm differentiates into the corneal epithelium on day 13. Intriguingly,
telocytes were visible within the epithelium. The secondary stroma develops
on the sixteenth day of gestation by differentiation of keratocytes. At the age of
2 weeks, the lamellae of collagenous fibers become highly organized, and the stroma
becomes avascular, indicating that the cornea has become transparent. Bowman's
membrane appears on day 23 of pregnancy and disappears on day 30. The Descemet's
membrane appears at this time and continues to thicken postnatally. The corneal
endothelium appears on the twentieth gestational day as double layer of
flattened cells and becomes a single layer of cuboidal cells on day 30. The spaces
between the endothelial cells resemble craters. VEGF immunohistochemical expression
increases over the course of development, reaching its peak in the first week
after birth before decreasing in all corneal layers and becoming negative in the
stroma. In conclusion, numerous morphogenetic events contribute to corneal maturation
and transparency, allowing the cornea to perform its vital functions

The development of the cornea is a fascinating process. Its dual origin involves the
differentiation of surface ectoderm cells and the migration of mesenchymal cells of
neural crest origin. This research aimed to demonstrate the morphogenesis of the
rabbit cornea from fetal to postnatal life using light- and electron microscopy, and
immunohistochemical analysis. There were 27 rabbit embryos and nine rabbits used.
The rabbit cornea begins its prenatal development on the twelfth day of gestation.
The surface ectoderm differentiates into the corneal epithelium on day 13. Intriguingly,
telocytes were visible within the epithelium. The secondary stroma develops
on the sixteenth day of gestation by differentiation of keratocytes. At the age of
2 weeks, the lamellae of collagenous fibers become highly organized, and the stroma
becomes avascular, indicating that the cornea has become transparent. Bowman's
membrane appears on day 23 of pregnancy and disappears on day 30. The Descemet's
membrane appears at this time and continues to thicken postnatally. The corneal
endothelium appears on the twentieth gestational day as double layer of
flattened cells and becomes a single layer of cuboidal cells on day 30. The spaces
between the endothelial cells resemble craters. VEGF immunohistochemical expression
increases over the course of development, reaching its peak in the first week
after birth before decreasing in all corneal layers and becoming negative in the
stroma. In conclusion, numerous morphogenetic events contribute to corneal maturation
and transparency, allowing the cornea to perform its vital functions.

The retina consists of various cell types arranged in eight cell layers and two membranes
that originate from the neuroectodermal cells. In this study, the timing of differentiation
and distribution of the cellular components and the layers of the rabbit
retina are investigated using light and electron microscopy and immunohistochemical
techniques. There were 32 rabbit embryos and 12 rabbits used. The rabbit retina
begins its prenatal development on the 10th day of gestation in the form of optic
cup. The process of neuro- and gliogenesis occurs in several stages: In the first stage,
the ganglionic cells are differentiated at the 15th day. The second stage includes the
differentiation of Muller, amacrine, and cone cells on the 23rd day. The differentiation
of bipolar, horizontal, and rod cells and formation of the inner segments of the
photoreceptors consider the late stage that occurs by the 27th and 30th day of gestation.
On the first week of age postnatally, the outer segments of the photoreceptors
are developed. S100 protein is expressed by the Muller cells and its processes
that traverse the retina from the outer to the inner limiting membranes. Calretinin is
intensely labeled within the amacrine and displaced amacrine cells. Ganglionic cells
exhibited moderate immunoreactivity for calretinin confined to their cytoplasm and
dendrites. In conclusion, all stages of neuro- and gliogenesis of the rabbit retina occur
during the embryonic period. Then, the retina continues its development postnatally
by formation of the photoreceptor outer segments and all layers of the retina
become established.

Several morphogenetic sequences occur during esophageal development and birth
defects occur due to defects in foregut morphogenesis. This work aimed to record
the cellular events in the morphogenesis of rabbits' esophageal epithelium. On the
16th day of gestation, the esophageal epithelium varied from stratified ciliated columnar
to stratified squamous type. The surface epithelium presented mucous cells with
mucigen granules of various sizes occupying their supranuclear cytoplasm. Cytoplasmic
vacuolation was evident in all layers of the esophageal epithelium at this age. On
the 18th gestational day, some light cells could be detected in the middle portion of
the epithelium, while others occupied the whole epithelial length. On the 21st day,
mucous cells are more frequently observed at the apical esophageal part as well as at
the surface epithelium. Numerous elongated dark cells could be distinguished embedded
between the basal cells. On the 24th gestational day the number of the mucous
cells reached its peak. Reaching the 30th gestational day, several lamellar bodies, a
keratinized layer and mitotic divisions could be demonstrated, and the number of
both mucous and dark cells was greatly decreased. Collectively, detection of surface
mucous and dark cells together with the non-cornified surface in some regions of the
rabbit esophageal epithelium at the end of gestation ensure a postnatal development
to reach the adult epithelium essential to sustain the passage of the harsh raw food.
Future immunohistochemical studies are recommended to investigate the components
of secretions in mucous cells and functional studies to highlight the dark cells
significance.

The development of the glandular stomach was studied using light, electron, and fluorescent
microscopy. The research used 130 Japanese quail eggs from the second to the seventeenth days of
incubation.The proventriculus could be distinguished on the3rd day. Its wall consisted of four tunics:
tunica mucosa, very thin tunica submucosa, tunica muscularis, and outermost tunica serosa. Mucosal
folds appeared on the 8th day. The luminal epithelium was pseudostratified columnar in type and
transformed into simple columnar by the 10th day. The mucosal papillae emerged on the 11th day,
spiraled on the 15th day, and had a distinct whorled look by the 17th day. Two types of proventricular
glands were recognized: compound tubuloalveolar and simple tubular glands. Both types were
situated within the tunica mucosa. On the 4th day, the compound glands emerged as evaginations
of the lining epithelium. It began to branch on the 8th day and became well established by the 11th
day. The simple glands appeared on the 11th day as localized down-growths of the luminal epithelium
forming solid cords. On the 15th day, many of them showed complete canalization. On the 8th day,
the muscular coat was differentiated into the lamina muscularis mucosae and tunica muscularis.