Journal of morphology . nervous system, and is in all cases onthe basal side of the ectoderm. Without demonstrating thepoint absolutely the embryological evidence is that the spongi-oblasts throughout the nervous system are much the same —forming Mullers fibres and the retina, and Deiters cells in thebrain and spinal cord. And as the evidence is graduallyaccumulating we must admit that the prolongations of thespongioblasts do not communicate directly but only come in. 42: MALL. [Vol. VIII. apposition, so that the same principle applies to them as to thenerve-cells, or to cells in general. Fig.
Journal of morphology . nervous system, and is in all cases onthe basal side of the ectoderm. Without demonstrating thepoint absolutely the embryological evidence is that the spongi-oblasts throughout the nervous system are much the same —forming Mullers fibres and the retina, and Deiters cells in thebrain and spinal cord. And as the evidence is graduallyaccumulating we must admit that the prolongations of thespongioblasts do not communicate directly but only come in. 42: MALL. [Vol. VIII. apposition, so that the same principle applies to them as to thenerve-cells, or to cells in general. Fig. 5 is a stage two clays in advance of Fig. 4. The fatglobules in this case show how the peripheral end of the cell isbreaking up into its prolongations. The process is beginningto effect the basal end of the cells also. Practically all thecells of the retina in this stage contribute to the formation ofthe net-work of interlocking cells, and as yet no true nerve-cells are present. In a stage later, Fig. 6, the lens is. Fig. 7. — Section through the eye of Amblystoma (8 mm. long) nine days beforehatching. X 133 times. S, spongioblast ; N, neuroblast. separated from the ectoderm, and the secondary optic vesicleis more cup-shaped. The net-work of fibrils is still outlinedby the pigment granules and they form such an intimatemeshwork that it is impossible to separate the cells. Thereseems to be a complete union of protoplasm of the cells, buton account of the mode of development as well as on accountof histological principles I consider this only apparent, and notreal. Already in this stage some of the nuclei are beginningto move towards the free border of the retina, and this isgreatly increased a day or two later (Fig. 7). No. 2.] HISTOGENESIS OF THE RETINA. 423 At this time the whole eye has advanced in its development,and in its centre the complete thickness of the retina is filledwith cells. Cells arising from the germinal layer have movedthrough the fine net-work of the pr
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