Figure 2. SEM and thin-section TEM of ball-and-sockets in the embryonic and adult chicken lenses. A: In the embryonic chicken lens (E18), a representative scanning electron micrograph showing many ball-and-sockets distributed on the short sides of superficial cortical fibers at the equatorial region (approximately 100 μm from the surface). B: At higher magnification, the height and shape of the ball-and-sockets can be readily visualized from side-view. C: In the adult chicken lens (P42 weeks), numerous ball-and-sockets are seen distributed in rows on the two long sides of superficial cortical fibers at the equatorial region (approximately 200 μm from the surface). It is estimated that the number of ball-and-sockets (approximately 13 ball-and-sockets per 100 μm² membrane) is not significantly different at the apical, equatorial and posterior regions along the anterior-posterior axis of any given superficial fiber cell. The border between two long-side fiber cells is marked by two arrows. Note that the height and the shape of these top-viewed ball-and-sockets cannot be readily appreciated as compared with those seen from the short sides in A and B. D: Thin-section TEM shows a ball-and-socket with the head and neck portions protruding into an adjacent cell. This ball-and-socket is completely occupied by a gap junction (gj). E: A cross-section of the ball-and-socket gap junction showing a considerable membrane extension of this junction into a narrow fiber cell. In the images, b is the ball, and s is the socket. The scale bar indicates 5 μm in A, C, 2 μm in B, and 200 nm in D and E.