Dvelopment of the Harderian gland in the chicken: light and electron microscopic investigations.

The Harderian gland of the chcken develops from epithelial cones of the conjunctiva between the 11th and 12th day of embryonal life. The development of the organ proceeds in two phases. During the stage of epithelial development (days 13 to 17 of embryonal life) the acinar epithelium differentiates into a lumen-adjacent glandular epithelium, and a separate layer of basal epithelial cells. This basal layer is initially compact but later forms a loose meshwork. The basal cells differ from the myoepithelial cells found in the Harderian gland of rodents by virtue of their smaller number of myofilaments; and they resemble the reticuloepithelial cells in the Bursa of Fabricius. On days 17 and 18 of embryonal life the interstitial tissue is invaded by eosinophils and by small 'blasts', up to 4 microns in diameter, both of vascular origin. Between days 17 and 20 the glandular epithelium undergoes secretory transformation. At the time of hatching (day 21), the secretory function is fully developed. The mode of secretion is partly apocrine, partly merocrine. During the following phase of plasmacellular development (from day 17 of prenatal until day thirty of postnatal life) interstitial plasma cells are formed from the immigrant small 'blasts'. Their number increases until the fourth week after hatching; thereafter the plasma cell population remains stable.