ABSTRACT
The eyecup movements of the common shore crab, Carcinus maenas L., have been recorded in two dimensions.
Saccades and eyecup drift occur in all directions. Eyecup tremor is a complex irregular movement although horizontal tremor predominates in most crabs.
Although the response to the movement of the light in a circle is usually an approximate circle or ellipse, rectangular responses are occasionally obtained and the eyecup often moves in a stepwise fashion in response to a smooth diagonal movement of the light.
The angle of response to a diagonal movement depends on the ratio of the response to horizontal and vertical movements alone. The eye is virtually stabilized in all planes by a contrasting object but never fixates upon a moving stimulus.
No torsional or twisting movements of the eyecups were obtained in response to light stimuli.
