It is in reference to the structure of the retina and vitreous body of the complex eyes that I have found myself unable to come to the same conclusions as Claus and Schewiakoff. Since the work of the latter goes much further into the detail of the subject than does Claus’s paper, it will be sufficient for me to compare my results simply with those of Schewiakoff.
The latter finds that the retina is composed of two kinds of cells, corresponding to the supporting and sensory cells referred to in the description of the nerve ring. These he figures (’89, Taf. II, Figs. 12 and 13) as alternating regularly. The two kinds of cells differ as follows:
(1) Shape. The supporting cells like those referred to before, are cone-shaped, having a proximal fibrous process that runs into the underlying stratum of nerve fibres, and on the surface of the retina a broad distal pigmented termination. The sensory cells are spindle-shaped, the proximal processes becoming continuous with fibres of the underlying nervous mass, while the distal process runs up to the surface of the retina (the part toward the lens) in between the ends of the supporting cell. The two kinds of cells are accordingly designated as pigment and visual.
(2) Position of nucleus. This comes in as a corollary of the shape. The nuclei of the visual cells lie in the enlarged central part of the spindle-shape, and, therefore, at a lower level than the nuclei of the alternating pigment cells.
(3) Processes in the vitreous body. The distal processes of the spindle-shaped visual cells are continued through the vitreous body to the cells of the lens as rod-like visual fibres which lie in canals in the (supposedly) homogeneous vitreous body. The pigment cells on the other hand have no fibres passing from them through the vitreous body, but in the latter are situated cone-shaped masses of pigment whose bases rest upon the broad ends of the pigment cells without, however, being a part of the cell.
(4) Pigment. The distal ends of the pigment cells in the retina are strongly pigmented, as the name implies. The processes of the visual cells, which alternate with these, are pigmented likewise, but the pigment is not so abundant and lies in the periphery of the cell body, leaving free a highly refracting central axis.