CRYSTALLINE LENS. 87 
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 laminz 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 lie 
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 poimt 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 
