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| Stannius corpuscles (SC) are unique endocrine gland in the kidney of bony fish. It plays an important role in regulating calcium haemostasis via secretion of hypocalcine (stanniocalcin) hormone. The structure of Stannius corpuscles has been clarified in several fish species; however, little was elucidated concerning that in African catfish (Clarias gariepinus). Therefore, the aim of the current study is to reveal the structural characteristics of SC in African catfish (Clarias gariepinus) among both sexes. Histological and ultrastructural examinations of SC were revealed among both sexes. The SC were paired, oval white colored bodies embedded in the trunk area of posterior kidneys. Histologically, the SC were surrounded by thin connective tissue (C.T) capsule from which many septa were extended dividing the glands into incomplete lobules. The parenchymal cells consist of two types; one with intensely eosinophilic cytoplasm and the other were weakly stained. Interestingly, the proportion of cells was varied among male and female. The female showed significant higher percentage of lightly eosinophilic cells than the intensely stained cells. On the other hand, the predominant cell type in male was the intensely stained one. Transmission electron microscopic observations revealed the presence of two types of cells; predominant type I (electron dense and electron lucent cells) and type II. The former showed more secretory granules than the later. In conclusion, our results revealed sexual differences in the proportion of cells and suggested that the type I could be responsible for hypocalcine hormone secretion. However, further investigations are required to reveal the structure of SC among different seasons.

The objective of this work was to study the histological structure of the dog's coronary artery by light and transmission electron microscope (TEM). The coronary artery consisted of three tunics: tunica intima, tunica media and tunica adventitia. The tunica intima consisted of endothelium rested directly on internal elastic lamina without the subendothelial connective tissue layer. The tunica media were composed of smooth muscle fibres interspersed with few elastic and collagen fibres. The tunica adventitia consisted of collagen and elastic fibres intermingled with fibroblast cells; it had vasa vasorum and nervi vasorum. Some histomorphometric measurements were performed and compared statistically. The ultrastructural study showed that the endothelial cells were communicated through complex junctions and characterised by filiform cytoplasmic processes passed through the opening of the underlying internal elastic membrane. The smooth muscle fibres of tunica media communicated with each other through cytoplasmic processes. The tunica adventitia showed minute non-myelinated nerve. This work revealed that the dog's coronary arteries are typical muscular arteries, which show little structural variations from that of other mammals. K E Y W O R D S coronary arteries, dog, histology, transmission electron microscope, tunica intima | 81 KILANY et AL.

The aim of this research work was to study the histological structure of the pancreatic acini by transmission electron microscope in two avian species, duck and pigeon. The specimens were collected and processed for electron microscopic study. The results showed that the acini of the two avian species were two types; the first one was an electron dense and the second one an electron lucent. The light acinar cells were larger in size than the dark cells. These cells contained centrally located ovoid nuclei with prominent nucleoli and abundant euchromatin. The cytoplasm was electron lucent, with many rough endoplasmic reticulum, polymorphic mitochondria. Numerous zymogen granules were distributed in the basal part and around the nucleus, so these cells considered active cells. The dark acinar cells were characterized by an electron dense cytoplasm. The most prominent cell organelle in these cells were the zymogen granules that appeared in different sizes while other organelles as mitochondria, and rough endoplasmic reticulum were inconspicuous or few, so these cells were considered as inactive cells. The nucleus with indented nuclear membrane located centrally with prominent nucleoli and abundant heterochromatin. Prominent intercellular spaces between the individual acinar cells, as well as well‐developed basement membrane separating the electron dense cells and the lumen contained the secretion between acinar cells. It could be concluded that the acinar cells in ducks and pigeons were divided into two types, that is, light and dark acinar cells which mainly attributed to the activity of these cells.