The Basement Lamella of Amphibian Skin

The basement lamella under the epidermis of amphibian larvae shows a sub-microscopic architecture of remarkable geometric regularity: It consists of about twenty layers of ground substance in which cylindrical fibers (presumably collagenous) of about 500 Angström diameter are embedded parallel to one another, but with the fiber directions alternating by 90 degrees from layer to layer. The repair of this membrane after wounding was studied electronmicroscopically in ultrathin sections. The sequence of events is as follows: (1) Epidermal cells cover the wound exudate by migration. (2) Rather uniform fibers of small size (<200 A) appear in the space between the epidermal underside and the subjacent fibroblasts; these fibers are sparse and oriented at random. (3) Proceeding from the epidermal surface downward, a wave of organization spreads over this primitive fiber tangle, resulting in the fibers becoming (a) straightened; (b) oriented; (c) packed into the characteristic layered structure; and (d) brought up into the 500 A diameter class.