I think that these prisms and fibres are the direct continuations of retinal cells. In a section such as that drawn in Fig. 63, which takes just the very tops of the cells of a slightly pigmented retina, in the centre of the section just grazing the space that lies between the retina and the shrunken vitreous body, most of the cells toward the middle (where especially the extreme tips are taken) show in their centres a dot exactly corresponding to the dots in the polygonal areas of the vitreous body. In the exact middle of the section, where only the cell walls appear, slightly indicated, a dot is seen in each case. The size and shape of the ends of the cells correspond with those of the polygonal areas in the vitreous body, and I do not doubt that the latter are continuations of the former. The vitreous body, then, instead of being homogeneous, is composed of the clear highly refracting outer ends of retinal cells. The assumption lies near that these are the true visual rods, but of course it is assumption only.
To give a brief review, the points in which my conclusions differ from those of Schewiakoff are as follows: I find (1) that the long pigment streaks are parts of retinal cells continued into processes like his visual rods; (2) that the vitreous body is composed of prisms with central fibres proceeding from retinal cells; (3) that I am unable to get satisfactory evidence of two types of cell distinguishable within the retina, and at any rate find considerable evidence against the two types he distinguishes.
These results are not wholly satisfactory, for they leave us with three kinds of fibrous processes in the vitreous body which for the present we are unable to trace to three, or even two distinguishable types of cell in the retina. It would be more pleasing if we could confirm Schewiakoff’s simple conception of the structure, with its one set of visual rods in the vitreous body referable to a clearly marked type of sensory cells in the retina, but I think the evidence that has been brought up justifies the conclusion that in some respects he saw too much, in other respects too little. This is not to be wondered at, since his material, to judge from a single statement, consisted of but twelve marginal bodies, and, moreover, the work on Charybdea forms but one portion of a paper that is excellent for the clearness of its descriptions and illustrations.