[Ultrastructural studies of visual cells in the human fetus]

The retinas of 15 human fetuses 14 weeks to full gestation were observed by transmission electron microscopy, with the findings that rod cells and cone cells were indistinguishable in the 3rd month of fetal age, and the outer segments were not developed while the centriole was discernible in the apex of the ellipsoid. During the 4th month of gestation, cilia grew from the centriole towards the pigment epithelium. In the 5th month, primordia of the outer segment began to form. The outer segment continued to elongate during the 6th month, but the membranous discs in the outer segment were in disorder and not uniform. During the 7th month, the outer segment increased in length, the cell increased in size and the cell organelles increased in number. After the 8th month of gestation, old membranous discs began to come off for neogenesis.