PHYSIOLOGIGAL ACTION OF LIGHT. 161 
the various parts in their natural position, then to carefully cut away the anterior 
and posterior portions of the brain, leaving only the middle portion in contact 
with the optic nerve. On placing this preparation between the clay points, so 
that the one touches the surface of the cornea, while the other is in contact with 
the brain substance, a strong deflection is obtained which is sensitive to light, 
and follows the course observed in the case of the frog. 
2. The Pigeon.—The effect was also traced into the optic lobes of a living 
pigeon (deeply under chloroform), the head of which was securely held between 
the clay points of the electrodes. The optic lobes in the pigeon are easily 
exposed. The following were the effects of this observation :—a, When one 
pole was applied to the left optic lobe, and the other to the cornea of the 
right eye, a deflection was obtained which was sensitive to light; 6, when the 
pole was removed from the right eye, and applied to the cornea of the left, a 
smaller deflection was obtained, also sensitive to light; and, c, when light was 
allowed to impinge on both eyes, while the one pole was in contact with either 
eye, and the other with the left optic lobe, the result was nearly double that 
produced by the impact of light on one eye alone, either right or left. These 
effects may be explained by the decussation of the optic nerves in the optic 
commissure. 
XI1.— EXPERIMENTS ON THE EYES OF FISHES. 
The subject was examined in the case of three fishes—(1), the gold fish 
(Cyprinus auratus) ; (2), the rockling (Motella vulgaris) ; and (3), the stickle- 
back (Gasterosteus brachurus). 
1. The Gold Fish.—With the eye of this fish a deflection of about 600° was 
obtained with the smallest possible contact. On the impact of light it rose 50°, 
remained steady for a short time, and then slowly sank. On removal it fell 
about 8° or 10° below the starting point. 
2. The Rock Fish—Specimens of this fish were obtained from the rock-pools 
in the neighbourhood of Kinghorn in Fifeshire. The deflection was similar in 
amount to that of the gold fish, but the variations occurred in a much longer 
period of time. 
3. The Stickleback.—The species examined is that frequently met with in 
brackish pools, a little beyond the level of high-water mark, at the sea-side. 
The eyes examined were very small. A deflection of 400° was obtained, which 
was remarkably sensitive to light, the variations occurring in very short periods 
of time. 
On comparing these results, it will be seen that, in the active and alert 
stickleback, the variations occurred rapidly ; in the more sedate goldfish, they 
occurred more slowly, while, in the case of the sluggish rockling, which hides 
beneath stones near low-water mark, the variations occurred very slowly. 
VOL. XXVH. PART I. 2,8 
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