c. In the vitreous body a cone-shaped streak of pigment overlies each pigment cell of the retina, which is not a part of that cell.
d. Apart from these pigment streaks and the rod-like processes of the visual cells the vitreous body is structureless, probably a secretion of the pigment cells.
My own work, now, has led me to a different conception, so that my conclusions on the same points would be as follows:
a. There is not good evidence of an alternation of cone-shaped pigment cells and spindle-shaped visual cells, with the nuclei of the latter at a lower level than those of the former.
b. From some of the retinal cells otherwise not distinguished, there extend rod-like processes into the vitreous body, such as described by Schewiakoff.
c. The cone-shaped streaks of pigment in the vitreous body belong to the underlying pigment cells, in fact are direct continuations of them, and at their distal ends they are prolonged into fibrous processes lying in canals of the vitreous body exactly like the visual fibres of Schewiakoff.
d. The vitreous body is not a homogeneous secretion, but is composed of prisms of refracting substance, each with a denser central fibre.
Let us go over these four points in detail.
(a) As to the first, the question whether there is an alternation of pigment and visual cells, I am not prepared as yet to make a positive statement, since my not seeing both kinds as they are described has little evidential value against the fact that Claus and Schewiakoff both claim to have seen them. Perhaps proof could be obtained one way or the other by maceration of fresh or of specially prepared material, which none of us had. My evidence for not confirming alternation rests wholly upon sections. [Fig. 58] represents a radial section through part of the larger eye of Charybdea, made from an osmic preparation which in this case showed two advantages over the material fixed in corrosive-acetic (usually by all odds the best), namely, that the vitreous body (vb) was not shrunken away from the retinal cells, as almost invariably happens, and that the retinal cells were contracted apart from one another in some places in such a way as to be almost equal to a macerated preparation. Now, in the figure it is seen that there is an apparent alternation of two kinds of cells, more regular than I usually find, but the ones that are undoubtedly the pigment cells of Schewiakoff are the ones that show the fibrous processes like his visual cells, and the pigment streaks in the vitreous body are seen to be integral parts of the cells, not cone-shaped masses lying in the vitreous body, merely associated with the pigment cells. If these are the pigment cells of Schewiakoff, the shorter cells in between must be his visual cells, yet they can by no means be said to conform to a spindle-shaped type, nor are their nuclei always at a lower level than (that is, internal to) those of the pigment cells. If the long cells with the fibres are, on the other hand, considered the visual cells of Schewiakoff, then again we find nonconformity to a spindle-shaped type, and nuclei not always at a lower level. The matter of alternation of nuclei at different levels seems to me any way too slight a distinction upon which to base a difference in function. It is a necessary mechanical consequence of the crowding together of many cells on one surface. And in many cases in perfectly radial sections through the retina I find the nuclei fewer in number and arranged in very nearly a single level. The retina of the smaller eye represented in [Fig. 69] shows this. In sections further along in the same series the nuclei are found at different levels, due without doubt to the slanting cut.