Fig. 4

Development of digits and the sixth protrusion in X. tropicalis. a–d, Digit development in the X. tropicalis hindlimb. a, c, Cartilaginous primordium of the sixth protrusion was detected at stage 55 (shown by arrowhead). b, d, Two elements of the protrusion were detected at stage 56. (c) and (d) are high magnification images of those in (a) and (b). Arrowheads and dotted lines indicate cartilaginous elements of the protrusion. e, f, Development of digits and the prehallux in the X. laevis hindlimb. At stages 55 and 56, cartilaginous condensation for the prehallux was undetectable. g, Condensation began at stage 57. h–j, External appearance of the protrusion at stage 57 (h) and stage 58 (i, j). j, A high magnification image of the protrusion in (i) that shows a clear, pigmented claw. All images are ventral views. Scale bars: 250 μm in (a, b, e–g) and 1 mm in (h, i)