Cytologic Features and Cellular Migration in the Cortex and Medulla of Thymus in the Young Adult Rat.

Dustin and Auerbach7 considered that lymphocytes initially arose from the el)ithelium of the thymus anlage, while Maximow thought they were derived from associated mesenchymal cells.8 In the adult thymus, the lymphocytes would come chiefly from divisions of preexisting lymphocytes and occasionallv from reticular ceIls2,6,M ( which may he either epithelial or mesenchyrnalt’). In the course of our own investigations on the derivation of lymphocytes,’0’1 1 a need was felt for precise information on the structure of resting and dividing cells in thymus. The cells were, therefore, observed and described in both the cortex and medulla of thymus in young adult rats. Some of the observations 1)rovided clues as to how lymphocytes are formed in thymus and released to the circulation.