Miscellaneous. : 149 
organs by observing a number of these animals which were ex- 
posed in large basins for sale at Naples. A shadow cast by his 
hand caused the extended siphons of the specimens on which the 
shadow fell, instantly to retract, while those not in the shadow re- 
mained extended. Repeating this experiment at the Zoological 
Station at Naples, and being fully convinced that the retraction 
was due to the shadow and not to a slight jar which might have been 
the cause, he was led to examine the siphon more closely, and he 
also made a series of vertical sections for the purpose of very minute 
study. 
When the siphon of a large Solen is cut open and examined, a 
number of fine blackish-brown lines or fine grooves are seen. These 
are situated between and at the base of the short tentacular pro- 
cesses of the external edge of the siphon. As many as fifty of these 
little grooves were found to be present in some specimens, and some 
of them were from | to 1°5 millim. in length. 
When a vertical section is examined these pigmented grooves are 
distinctly seen, and the cells of which they are composed are very 
different from the ordinary epithelial cells which cover the more 
pigmented parts. These latter cells are ordinary columnar epithelial 
cells with a large nucleus which is situated near the tunica on which 
it rests. The pigmented cells are from one third to one half longer 
than those just described, and consist of three distinct parts. The 
upper part, or that part furthest from the tunica, appears perfectly 
transparent and takes up about one ninth or one tenth of the total 
length of the cell; this part is not at all affected with the colouring- 
matter used in colouring the whole. The second part of the 
cell is deeply pigmented and consequently opaque; it is filled 
with a dark brown or almost black granulated pigment; this takes 
up about one half of the length of the cell. Below this is the third 
part of this cell, consisting of a clear mass, which takes a slight tinge 
when coloured ; this is probably the most active part of the cell; in 
this is imbedded the large oval nucleus. This nucleus is sharply 
demarcated and is filled with a granulated matter, which takes a 
dark colour in borax carmine, as do, indeed, the nuclei of all the 
epidermal cells. 
These retinal cells, if they may be so called, are similar to those 
described by P. Fraisse in 1881 (Zeitschr. f. wiss. Zool., Bd. xxyv.), in 
the very primitive eye of Patella cwrulea, the principal difference 
being that in Patella the transparent part at the top of the cell 
seems to be a little more extensive. This eye of Patella is open, 
being merely an invaginated part of the epidermis, and has no lens, 
In Haliotis tuberculata we find an open eye also, but with the addi- 
tion of a very primitive lens. The next higher grade of eye seems 
to be that of Fisswrella rosea, in which the eye is closed and pos- 
sesses also a lens; now in these two latter forms, where we find a 
lens present, the retinal cells do not possess the transparent ends 
we find in Patel/a and Solen, but the pigment fills the upper part 
of the cell quite to the top. This would indicate, he thinks, that the 
transparent part took the place of a lens, 
