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Take out both the lens and the iris and the choroid coat of the eye will reproduce both. We are in the A, B, C class in powers of repair by comparison with the angleworm, the lobster, or the salamander.
*The Inner Coat, or Retina.*—This is a delicate membrane containing the expanded termination of the optic nerve. It rests upon the choroid coat and spreads over about two thirds of the back surface of the eyeball. Although not more than one fiftieth of an inch in thickness, it presents a very complex structure, essentially nervous, and is made up of several distinct layers.
This pigment membrane clothes, not only the inner surface of the choroid proper, but also the hind surface of its anterior muscular continuation, which covers the edge of the lens in front as a circular membrane, and arrests the rays of light at the sides. The circular opening that is left in the middle is the pupil, through which the rays of light penetrate into the eye.
The retina contains curious structures which can be seen only with the aid of the microscope. For instance, a layer near the choroid is made up of nerve cells arranged in innumerable cylinders called "rods and cones," and packed together not unlike the seeds of a sunflower.
The smaller segment, which forms about one sixth of the whole, is set upon the larger and forms the projecting transparent portion in front. Yellow spot. 2. Blind spot. 3. Retina. 4. Choroid coat. 5. Sclerotic coat. 6. Crystalline lens. 7. Suspensory ligament. 8. Ciliary processes and ciliary muscle. 9. Iris containing the pupil. 10. Cornea. 11. Lymph duct. 12. Conjunctiva. 13.
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