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The structure of the bursa of Fabricius in wild birds.

The bursa of Fabricius of wild birds, especially that of Passerine birds was investigated, and it was established that there are two types of structures in the mucous membrane, i.e., the plica type and the tubulus type. The development and structure of the lymph follicle in each type were discussed. Morphological correlation between the bursa and the cecum was observed, and these results were collectively arranged in a table. It was also mentioned that the variations of the structure of the BF should be taken into consideration in future when the function of the BF of birds are discussed.The author wishes to express his gratitude to Mr. Eiichi Sato, Akita Prefecture, for the sincere help in collecting the materials.