CRYSTALLINE LENS.
fibres which lie close together in the first instance, do not, as it seems, continue connected with one another, a portion of the original table must be absorbed, and the following may therefore be conceived to be the mode in which the fibres originate. After the two laminae of the table are in part or entirely blended together, an absorption takes place at certain parts, in such a manner, that the portions not absorbed lie in longitudinal lines, and thus remain as fibres. The reality of an absorption is, moreover, distinctly shown by the disappearance of the cell-nucleus. We have no evidence as to whether the fibres are hollow or not; it is sufficient for our purpose to know that they originate by a transformation of cells.
The quill of the feather has a similar structure to that of the cortical substance of the shaft.
The vane is composed of separate barbs, and each barb is again a miniature feather. The following description is taken from the undeveloped wing-feather of a sparrow. Each barb contains a secondary shaft, on the side of which is placed a secondary vane. ‘The secondary shaft has the same structure as the principal one, and consists of a cellular medullary sub- stance (pith), and a firm cortex. The secondary vane is com- posed of a great many triangles, which lie with their surfaces close together, having very narrow bases by which they are fixed upon the secondary shaft. Each triangle is formed of flat epithelium-cells arranged with their angles overlapping each other, each having its nucleus. The separate epithelium- cells are broadest below, diminish more and more towards the point, and extend proportionately in length. The nuclei le in a row, near about the middle line of the triangle. The last cell, at the apex of the triangle, is contracted into a long fibre. The last cell but one, and all the others in succession, become elongated, at the point at which the next following cell is attached to them, into pointed processes, which vary in length, and are extended on both sides of the cells in the plane of the triangle.
6. The Crystalline lens. The mode in which the lens is nourished has always been an enigma. Having no vessels, it has either been regarded as a secretion of its capsule, or its
