498 S. R. DETWILER AND HENRY LAURENS 
ment layer. Because of the fact that only the merest trace of 
cytoplasm can be shown to envelop the nucleus of the primitive 
visual cell, Cameron claims that the visual element cannot be of 
cytoplasmic origin, and he thus believes that it is compositely 
developed from the nucleus and from the ingested pigment of the 
epithelial layer. 
It seems to us that, even if pigment ingestion can be really 
observed, the fact must not be overlooked that pigment inges- 
tion could not take place unless there were cytoplasm present to 
ingest it. Cameron holds that the clear globule does the ingest- 
ing, but it so happens that the heavily stained granules which he 
saw, as well as those which we have observed, do not lie within 
the globule, but in the cytoplasm beyond it (fig. 3). Cameron 
himself remarks, ““ . . . . and the product of the ingestion 
of the pigment becomes deposited upon the summit of the glob- 
ule in the form of a substance which stains intensely with iron- 
alum-haematoxylin. In this manner, layer after layer becomes 
superimposed until all the visual elements without exception now 
assume the shape of cones, with the achromatic globules, much 
reduced in size, situated in their bases. ”’ 
From our observations the origin of the globule cannot be 
stated decisively, but whenever it is present, it is always sur- 
rounded by cytoplasm and the two seem to appear simulta- 
neously. In many initial developing cases, cytoplasmic buds can 
be seen in which there is no globule and yet they contain the 
heavy granules which are shown in figures 2 and 3. That these 
granules should represent products of epithelial pigment seems 
very doubtful from our observations. If they are ingested under 
the chemotactic influence of the globule, as Cameron says, then 
visual cell buds which lack the globule should be devoid of this 
deeply staining substance. Moreover, the pigment needles of 
the hexagonal cells are not stained nearly so heavily as are those 
in the visual cell buds. The former are brownish and only appear 
black when heavily massed. The granules in the visual cell bud 
are jet black in our preparations, even when appearing singly. 
Our observations suggest that the heavily stained granules are 
elaborated in the cytoplasm of the visual cell and that the globule 
