An account of a membrane in the eye, now first described

In this paper the author describes a delicate transparent membrane, covering the external surface of the retina, and united to it by cellular substance and vessels. Its appearance varies in the different classes of animals, and at different ages. In young animals it is transparent and tender; but in the adult firm, and stained by the pigment. In fishes, it has been described by Haller and Cuvier as the medullary layer of the retina; but the author thinks incorrectly, since it presents no character of nervous structure, and the retina remains perfect before it. The author concludes this communication by describing his mode of examining delicate anatomical structures:—He procures a hollow sphere of glass, between two and three inches in diameter, of which one fourth is cut off at the open part, and the edges ground so as to fit upon a plate of glass to which the object is attached and immersed in water; the sphere is then filled with water, and inverted over the object upon the plate. The whole being withdrawn from the basin the object may be examined, and the portion of the sphere filled with water furnishes a convenient magnifying power.