52 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 
I have found no evidence in these cells of the existence of an 
axial fiber such as I have described for the prism and pyramid cells. 
I find no definite arrangement of the nuclei of the retina into definite 
layers, but the nuclei of the three kinds of cells lie quite mixed, 
sometimes one kind lying deeper than the other as can be seen in 
the figures. Again, they may lie quite at the same level. (This 
point will be referred to later.) 
It is these long pigment cells that I believe retract their 
pigmented part from between the prisms and pyramids when the 
medusze are placed in the dark, protruding with their pigment 
when placed in the light. Fig. 5 is a section from a _ slightly 
pigmented retina killed in the dark. The parts of the cells pro- 
jecting beyond the pigmented zone, and which would lie between 
the prisms and pyramids (here not shown) of the vitreous body are 
seen to be narrower than in sections from retinas killed in the light 
(Figs. 1, 8, 4, 7) and the cells themselves appear in a condition of 
retraction as is shown by their large centrad portions with the nuclei, 
which latter, also, here lie at quite a lower level than the other nuclei. 
(The pyramid cells were not shown in this series.) I occasionally 
found appearances like Fig. 5 in retinas killed in the dark (indeed, 
in some the pigmented portions in the vitreous body were much 
thinner and more retracted than in Fig. 5). Yet this appearance 
was not of sufficiently general occurrence to leave no doubt as to 
its significance. As positive evidence, however, I cannot give it any 
other interpretation than the one given—that the cells retract 
themselves with their pigment when in the dark. Again, it must 
be added that the nuclei of these cells may occasionally lie quite 
deep even in retinas killed in the light. Indeed, lke structures in 
different retinas may vary considerably in size and shape. None 
of my darkness retinas, however, showed such a large proportion of 
the pigmented parts of the long pigment cells projected between 
the prisms and pyramids as did the light retinas. I examined 
and tabulated all my series with respect to the extent the long 
pigment cells were projected into the vitreous body, and I found 
that those which showed these cells with their pigment least 
projected between the prisms and pyramids to be those that had 
been killed in the dark. I thus feel satisfied that the pigmented 
parts of these cells become in part or quite completely retracted from 
between the prisms and pyramids of the vitreous body when in the 
