Chromatophore Responses in Relation to the Photoperiod and Background Color in the Hawaiian Ghost Crab, Ocyp ode ceratophthalma (Pallasy

phores are classified as morp hological when there is a change in the amoun t of pigment present over a period of time, and as physiolog-ical when there is a relatively rapid change due to changes in the degree of dispersion of the pigment. A pr imary chromatophore response is a response to a nonvisual stimulus, while a secondary response is a response to a visual stimulus (Fingerma n, 1963:8). Th e most common method of describing the degree of dispersion of the chromatophore pig-ments is that of Hogben and Slome (1931:12, fig. 1) using a one to five scale, where one corresponds to maximum concentration and five to maximum dispersion of the pigments, and the intermediate stages are described as two, three, and four. The present study deals with the ability of the H awaiian ghost crab, Ocypode ceratopb-tbalma ( Pallas) , to maintain a rhythmic physio-logical chromatophore response with different periods of light and darkness and on different backgrou nds