The reactions of certain mysids to stimulation by light and gravity

Abstract

Light-adapted mysids as exemplified byHemimysis lamornaedisplay phototelotaxis which regularly alternates in sign from positive to negative andvice versa. This reaction may be disturbed by other activities such as feeding; it only takes place in horizontal illumination.Dark-adapted mysids display negative geotaxis. When a light stimulus is given this geotaxis is reversed in sign irrespective of the direction of the incident light.When the statocysts of the mysids are removed their responses are much more like those of planktonic creatures. In the light normal orientation is maintained by the “dorsal light reflex”, and in darkness by the “general position reflex”. In the darkness a feeble negative geotaxis is sometimes seen. In light, phototaxis is seen in both light-adapted and dark-adapted conditions; in the majority of cases it is negative but on occasion has been seen to be positive.