The spleen is considered a key player in birds’ immunity. The stroma and the parenchyma of the spleen of the adult quail were demonstrated histologically, histochemically, and ultrastructurally. A thin capsule and the absence of trabeculae were the most characteristics of spleen stroma. The demarcation between white pulp and red pulp was not observed in the quail. White pulp formed from the periarterial lymphatic sheath and the periellipsoidal lymphatic sheath, both of which were surrounded by arteriole and ellipsoid, respectively. Ellipsoids appeared more numerous and were characterized by cuboidal lining of the epithelium and supporting cells. Red pulp consisted of sinuses and cords. White pulp and red pulp of the quail spleen contained various cells, such as red blood cells, macrophages, heterophils with characteristic granules, lymphocytes of different sizes, dendritic cells, plasma cells, and telocytes. In addition, closed circulation and open circulation established the blood flow on the spleen.

The adrenal gland is a vital endocrine gland that secretes many important hormones in everyday bird life. The adrenal gland of the Japanese quail is grossly located ventromedially the corresponding kidney and has a creamy to yellow color. The quail gland is surrounded by a capsule and contains some ganglionic cells, and the capsule is characterized by the presence of chromaffin cells. The adrenal gland is subdivided into three concentric zones: subcapsular, peripheral, and central. The parenchyma consists of interrenal tissue, chromaffin islets, and blood sinusoids. The interrenal cells contain lipid droplets, are arranged in cords, and rest on the basement membrane. Chromaffin cells are categorized as two types: epinephrine (E) and norepinephrine (NE) cells. These cells contain the granules, and are characterized by the presence of lipid droplets. In this study, the interrenal tissue was found to have a higher proportion of chromaffin cells in quail as compared with other birds, which is attributed to the fact that the Japanese quail is a migratory bird. Therefore, the present investigation aims to provide a detailed study on the adrenal gland in the Japanese quail to help physiologists understand the gland's function and the pathologist to determine the implications for the differential diagnosis of adrenal gland tumors. Highlights The adrenal gland is subdivided into three concentric zones: subcapsular, peripheral, and central. The interrenal cells contain lipid droplets, are arranged in cords. Chromaffin cells are categorized as two types: epinephrine (E) and norepinephrine (NE) cells. These cells contain the granules, and are characterized by the presence of lipid droplets. The interrenal tissue was found to have a higher proportion of chromaffin cells in quail because it is a migratory bird.

The health of oviduct circulation is very important for normal egg production. The present work describes the histology and histochemistry of vessels of different types on the oviduct of quail. Arteria, venae and lymphatics of the oviduct were described clearly. In addition, special vascular elements were observed presenting circular, longitudinal and oblique smooth muscle fibres on the blood vessel wall. Glomus cells were observed at typical glomus vessels, atypical glomus vessels and on the wall of some of arteria and arteriolae. Also, spirally oriented blood vessels were observed. Dark brown pigment was detected in the wall of arteria, venae, lymphatics and the special types of blood vessels.

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.

Rabbits have been proposed as a model for the human meibomian gland (MG), a large specific sebaceous gland in the eyelid that consists of secretory acini arranged laterally and related to the central duct via short ductules, with the central duct continuing as an excretory duct to open at the free margin of the lid. First detected at embryonic day 18 as an aggregation of mesenchymal cells in the tarsal plate, it completes its development approximately 2 weeks postnatal when the separation of the eyelids is completed. The Transmission electron microscopy supports the meibocytes’ gradient maturation to the meibum’s synthesis. While the differentiating cells, their cytoplasm, are well packed with lipid droplets, the basal cells are characterized by a high nuclear to cytoplasm ratio. The androgen and estrogen receptor proteins are expressed in the basal cell and the meibocytes, and increase in age increases in the expression of these proteins. Additionally, the cytokeratin (CK14) is expressed in the basal and differentiating cells of the acini and the ductal epithelium. Therefore, the duct cells of the MG are common in all stem cells. These data concluded that the MG plays a major role in maintaining the health of the ocular surface and preservation of visual acuity. Any abnormalities in the structure of the MG lead to its dysfunction and changes in lipid secretion.