Nov., 1902 .] Visual Area in Lampsida Ventricosus. 
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tact between nerve and epithelial cell would be needed for a 
demonstration, this spot has every appearance of being visual 
and the writer believes it to be such. 
The mantle was found by repeated experiment to be sensitive 
to both concentrated rays of light and to shadows. It was not 
determined whether the visual area was confined to one spot or 
generally distributed. 
A section through the eye like spot shows the epithlinm to- 
be greatly thickened, and much more pigmented than *the ordin- 
ary epithelial cells. The slightly pigmented epithelium is about 
15 micromillimeters thick while the eye spot is 60. 
The ordinary epithelium is pigmented throughout about half 
its length, the remaining basal portion of the cell being taken up 
with the nucleus, while in the visual cell the nucleus is 15 mm. 
long and the pigmented area 45 mm. long. 
The outer exposed end of the visual cell bears a well marked 
corneous like coat while this is almost absent from the surround- 
ing epithelium. 
In addition to these marked differentations, the basal ends 
of the visual cells are drawn out into branched processes which 
are about 15 mm. long. These extend down into the subjacent 
tissue and supply the place of a rather well defined membrane 
which exists between the ordinary epithelime and underlying tis- 
sue. While these processes have not been proven to be in con- 
tact with nerves, jet there is an undoubted visual area here. The 
modification of the ordinary epithelium into a heavily pigmented 
epithelinn and this finally into a visual area as in this form does 
not involve nearly so radical a change as has gone on in the devel- 1 
opement of the pallial eyes of pecten. The corneous lens like 
body is only a modified cuticle and any cell bearing pigment may 
be sensitive to light. 
The presence of so well defined visual area in one of our 
fresh water clam is a striking fact since the group as a whole 
seems to be entirely insensitive to light. 
