Inhibition of Pigment-Cell Migration in Triturus torosus

D URING the later embryonic and early larval stages of the urodele Triturus, melanoblasts, arising from the neural crest, migrate ventrally on the sides of the body and, as pigment forms, become visible in a definite pattern (Twitty, 1945). In Triturus torosus, as pigment formation renders the cells directly visible in the earlier larval stages, a dorsal band, consisting of numerous cells, appears on each side of the dorsal mid-line. Slightly later a relatively small number of the pigment cells constitute a more or less definite longitudinal cell series just dorsal to the border of the ventral yolk on each side of the body, posterior to the head region. Still others, almost always fewer in number, may remain scattered between this lateral series and the dorsal band. After an interval, in which little or no increase in number of these lateral pigment cells is evident, additional cells become visibly pigmented. In discussion of the behavior and the