Development of the pigeon bursa of Fabricius. A scanning and transmission electron microscope study

The development of the pigeon bursa of Fabricius was investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Particularly SEM emphasized that the bursa during development progressively undergoes hypertrophia and hyperplasia of lobules constituting the plicae. Moreover modifications of surface epithelium were observed. During early days of development after hatching, epithelium showed evenly distributed microvilli which become shorter and shorter and also unevenly distributed with aging. In addition TEM allowed us to state that the bursa of Fabricius in pigeons, during development, undergoes morphological modifications among which one of the most remarkable is the gradual and continuous increasing of lymphocytes. Another one, as it was already observed in chickens (Frazier 1974), consists in the contemporaneous but independent development of cortex and medulla, even if we observed undifferentiated epithelial cells moving from medulla to cortex and a migration of lymphocytes and mesenchymal cells from cortex to medulla (Tar et al. 1958; Ackerman et al. 1964; Naukkarinen et al. 1978).