Fig. 1H).
During the middle-eyed stage,
melanophores first appear above the
midbrain and subsequently behind
the midbrain–hindbrain boundary
(stage 8; Fig. 1G). In the subsequent
late-eyed stage, a line of dark pigment
cells appears that demarcates the horizontal
midline, and the mostly stellate
black pigment cells on the head
increase in number, size, and density,
and become more dendritic in their
appearance (stage 9; Fig. 1H). Different
regions of the embryo are often
covered by melanophores of different
shapes (Goodrich et al., 1944; Tavolga,
1949). Furthermore, paired dorsal and
ventral pigment lines emerge, followed
by a second, weaker horizontal
line of melanophores above and parallel
to the midline.