Comparative studies on the physiology of the iris.-II. Uranoscopus and Lophius

The reasons for supposing that the sphincter iridis muscle of this fish receives motor fibres from the sympathetic system and the dilatator muscle motor fibres from the oculomotor nerve have already been stated (Young, 1931). In that paper certain rough pharmacological tests were reported, and these have since been supplemented by more exact observations with the camera lucida method which are been recounted. In the earlier work it was concluded since no further movements of the iris were observed after section of both optic nerves that the direct effect of light on the sphincter muscle plays no part in the control of the pupil of Uranoscopus. This has been confirmed with the more exact methods. Dark adapted eyes were observed with a camera lucida. On illumination with a bright white light no movements were ever observed, although the magnification used (53X) allows of the certain detection of movement of 0·02 mm. Since the diameter of the pupil of a medium sized Uranoscopus is about 2·3 mm., the smallest detectable movement would be equivalent to a narrowing of 1/115 of the diameter. Within the limit, therefore, increased intensity of illumination causes no movements of the isolated iris.