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Abstract

Electron microscopic studies on thymus of layer chicken were done in various age groups ranging from day-old to forty weeks. The thymic gland in chicken showed a thin connective tissue capsule. In thymic parenchyma, lymphocytes or thymocytes, retiucloepithelial cells, myoid cells and macrophages were the predominant component and the other cell types occasionally observed were erythrocytes, granulocytes, mast cells and plasma cells. Three types of reticuloepithelial cells were observed. The Hassall’s corpuscles were composed of concentrically arranged reticuloepithelial cells. The centre of the corpuscles appeared either solid or cystic. The myoid cells were found mainly in the medulla. Intracellular and intercellular cysts were observed in association with the Hassall’s corpuscles in all the age groups. The onset of involution was observed in twenty week-old birds and marked involutary changes were noticed in forty weeks.