抄録
Thyroid glands of chick embryos from 7 to 20 days of incubation were studied with the electron microscope. In 7, 8 or 9 day-old embryos in which a colloid is not yet formed, the vacuole systems are not well developed in the epithelial cell. A few mitochondria, PALADE's particles and small GOLGI fields without large vacuoles are distributed throughout the whole cytoplasm of the secretory cell.
At 9-10 days when colloid-containing follicles and intracellular droplets of low density appear in the epithelial cell cords, the rough-and smooth-surfaced endoplasmic reticulum also becomes distinct. Sometimes the limiting membrane of this droplet continues with the rough-surfaced endoplasmic reticulum. This suggests that the granule of low density is produced in the rough-surfaced endoplasmic reticulum. Mitochondria observed near the outer surface of this reticulum might have also same function in manufacturing this droplet. On the other hand, the granule of high density is produced in the GOLGI vesicles. A typical apocrine secretory process is not observed in the embryonic thyroid of the chick.
Some of the colloid-containing follicles are produced by fusing of the intracellular colloid of one cell and that of an adjacent cell, while others are originated from the intercellular space.
A typical pericapillary structure consisting of two layers of basement membranes and pericapillary space between them is not distinct before 15 days of incubation.
