Development and Reactions of Melanophores of Embryos and Larvae of Typhlogobius Californiensis Steindachner

Abstract

Investigations concerned with the responses of the chromatophore system of the young of amphibians and fish have shown in most cases that this system passes through two physiological phases. The first response of the melanophores is to expand in light and to contract in darkness. This is believed to be a primitive reaction and the melanophores are assumed to be in the primary phase. Later in development and coincinding with the pigmentation of the eyes these melanophores show a reversal of their previous reaction, contracting in light and expanding in darkness, and are believed to be in the secondary phase in which the system remains throughout life. This reversal of the reaction to the primary phase response is believed to be due to the influence exerted indirectly by the eyes through the nervous system. This view was first emphasized by Babak (1910) and has since been confirmed by the experiments of Hooker (1914) on Rana pipiens, Laurens (1915, 1917) on Amblystoma, Fishel (1920) on amphibians, Duspiva (1931) on Salmo salvelinus and Perca fluviatilis, Tomita (1936) on Macropodus opercularis, Parker (1936) on Mustelus canis, and by Detwiler and Copenhaver (1940) on Amblystoma. It is to be noted that Parker records that the young of Mustelus omits the primary phase reaction to stimulation. According to a report of Coonfield (1940) the reactions of the melanophore system of the young of Pomacentrus leucostictus are at variance to those given in the reports previously cited. These young fish gave no consistant pigmentary reaction until a few hours before hatching. Beginning at this time and end'ng a few hours after hatching the melanophores of both the normal and the eyeless embryos and larvae contracted in response to a white background, expanded when over a black brackground, and contracted when in darkness. In view of these results and those of Parker previously cited, I decided to make further investigations of this problem of pigmentary responses of young fish. The young of Typhlogobius were selected because the eyes of this fish degenerate before they reach maturity, thus possibly giving some indication of the part taken by the eyes in the melanophore reaction.