Electron microscopic studies on zonule. Its origin and fibroblast.

Rabbit fetuses (14, 16, 17, 18, 20, 22, and 24 days in utero) were examined with an electron microscope, and the following results were obtained: 1. At the equatorial region of the lens, developing endothelium of the tunica vasculosa lentis was very similar in morphology to typical fibroblast. 2. Much debris of amorphous material was observed around the endothelium and fibroblast, but in general, zonule-like fine fibrils were seen near the former, whereas short collagen fibrils were observed around the latter amid amorphous material. 3. Topographically, fibroblasts lay apart from the lens equator, and few fibroblasts migrated into the posterior portion. 4. From the above data it was postulated that debris around the tunica vasculosa lentis in the vicinity of the lens equator was presumably the precursor of zonular fibrils and that fibroblasts had almost no relation to zonular formation.