In a majority of over 50 Fundulus majalis tested, the part of a previously faded primary denervated caudal band flanked by two new secondary bands showed pigment dispersal in its xanthophores, as if affected by the stronger dispersal in those of the adjacent secondary bands. The effect appeared whether or not the radial blood vessels were cut by the incision that produced the primary band. Intact control bands, flanked identically, generally gave no sign of a like effect.A few experiments on F. heteroclitus revealed comparable responses by its xanthophores.These observations derived from the xanthophores were paralleled by some from the melanophores in F. majalis.Characteristically, slow changes in the xanthophores in response to bottom color proceeded axipetally in primary bands, and they took place in secondary bands by an analogous invasion from the edge adjoining an innervated sector rather than from the edge of the primary band.Quick pigment concentration apparently excited by handling, holding on th...