CRYSTALLINE LENS. S7 



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 

 mav 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 bail) 

 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 lie 

 in a row, near about the middle line of the triangle. The 

 last ceil, 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. 



G. 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 



