Fine structural studies on the thyroid gland of the normal domestic fowl.

The ultrastructure of the thyroid gland of the domestic fowl has been investigated and found to be similar to that of mammals. The differences were found at subcellular level in the distribution of the "dark bodies" which were mainly apical and in the sizes of primary lysosomes. These were found to range from 100 to 500 nm in diameter. All organelles described in mammals as being concerned with the production of thyroglobulin and the two hormones thyroxine and triiodothyronine were found to be present.